Circuit.cellar.023.Oct Nov.1991

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English: EDITOR’S

The Forgotten Language?INK

Ken Davidson

I s the English language really so obscure that people have

iven up trying to use it correctly altogether? Granted, English is

ne of the more difficult languages to learn due to its endless

xceptions to rules. It’s usually more important to get your idea

cross than to get all the parts of the language correct. My

rustration stems from my recent observations of some so-called

editors” that can’t even catch a spelling mistake let alone bad

unctuation or grammar.

Werecently started the search for additional staff editors. All

hat we’re asking of these people is that they be able to read a raw

manuscript; fix spelling, punctuation, and grammar; and convert

ny “engineerese” into readable English. As part of the interview

rocess, we’ve been giving each applicant a test consisting of two

f the new product releases being used in this issue, and asking

hem to fix any mistakes they find. In addition to the problems

lready contained in them, I doctored each release with some

pecific mistakes that I was interested in. The results have been,

rankly, disappointing.

Most of the applicants had some form of English degree and

xperience in at least technical writing; many had some editing

ackground. Virtually everyone missed one or more blatant

pelling mistakes, and the vast majority of them missed many of

he planted punctuation, grammar, and usage mistakes. There

were even typos in some of the resumes and cover letters we

eceived (we didn’t call those people back). Luckily, we had a

andful of people that did fairly well, so we should be in good

hape when it comes time to make some offers.

I learned a long time ago while corresponding on computer-

zed conferencing systems that, regardless of what someone had

o say, if the message looked like hell-full of spelling and

unctuation mistakes-that person came across looking less

ntelligent than he probably was. We see it all the time on the

Circuit Cellar BBS, though no one corrects anybody since we are

more interested in what people have to say than in how they say

. We also, unfortunately, see it in article manuscripts as well,

where it is more important. That’s why we need the editor-one

who can fix the things that very few of the applicants have been

ble to fix-in the first place!

I’ll be the first to admit that there are mistakes between the

overs of every issue of CIRcurr CELLAR INK. No matter how many

airs of eyes look at each article, something always slips by. We

ust received a diatribe from an irate reader pointing out two

mistakes in a recent issue. One was in usage, the other in capitali-

ation. I was, of course, embarrassed when I saw them, since they

should have been caught early on. However, since he didn’t seem

to be able to find anything else wrong, I think two bad words out

of the thousands in the issue isn’t half bad. He could have a field

day with some other publications I see on the newsstand each

month.

I don’t expect our authors to be able to write prize-winning

articles; I certainly can’t. I also don’t want to discourage anyone

from submitting an article because they don’t think it’s good

enough; it can be massaged into something we can all be proud

of. What I would like to encourage, though, is that when writing

a piece, have someone else look at it to see if it even makes sense.

Run it through the spelling checker on your word processor for

obvious blunders. The more subtle things can be fixed later.

A FAREWELL

Why are we hiring new editors? The answer is twofold: we

need someone to help an already overworked staff, and we

recently lost our editor-in-chief, Curt Franklin, to another

(noncompeting) publication. Curt came to us three years ago

when CIRCUIT CELLAR INK looked like something a bunch of

engineers had thrown together (because that’s what it was). With

his guidance, CIRCUIT CELLAR INK has developed into a highly

regarded journal read and enjoyed both by engineers in some of

the finest companies all over the world and by those who simply

have a love of tinkering with computers. Curt will be sorely

missed, but life goes on, and we plan to continue to bring you a

first-class publication destined for the reference shelf after being

read cover to cover.

Oc tober /Novem ber 199 1 1







READER’SINK

Letters to the Editor

STANDARDS HOTBEDS

I seldom write a letter like this, but Steve’s editorial inthe August/September (#22) issue of CIRCUIT CELLAR INKis more than I can resist. It says, “Standards happened.. . bycommittees made up of competitors and large users, eachwith a particular axe to grind and no strong motivation forreal standardization.” Later, you remark (almost ruefully)that you have never served on a standards committee.

You should fall to your knees and thank God that Hespared you that horrible experience. In my lifetime I’veserved on two. The most recent was an I.F.A.I. subcommit-teeof the S.A.E., and I do not exaggerate when I say that theantics of most of the other members almost drove meinsane. Things degenerated to the point where I wasactually heckled in technical presentations. All because asmall minority wanted the S.A.E. to adopt without modifi-

cation a test procedure issued by I.S.O. that could be shownby theory and data to be worthless. Conversations withothers who had served on such committees convinced methat they are, almost without exception, hotbeds of politi-cal infighting.

Charles BoegliBlanchester, OH

DEVICE DRIVER NITS

I just received the August/September (#22) issue ofCIRCXJIT CELLAR INK and read Chris Ciarcia’s “Using De-vice Drivers to Change the Rules.” I enjoyed it very much.Based upon my knowledge gained from reading suchpublications as ‘The MS-DOS Encyclopedia,” I think thereare a few inaccuracies in his article. These are based uponmy familiarity with MS-DOS Version 3.3, however.

In the section “From The Top,” you explain how theBIOS ROM searches for extensions and “...marks themwith a unique byte sequence which identifies them asROM.” I believe that each ROM starts with a unique

“55AA” signature that is verified by the POST. Each such

extension is then called at its entry point just after thissignature to perform initialization. The POST can’t mark aROM, nor change any location in an extension it finds.

In addition, the ROM bootstrap does read in the firstsector of a disk. In the case of a floppy, this is the actualbootstrap code that attempts to locate and read IO. SYS

and MSDOS . SYS. However, on a hard disk that has mul-tiple partitions, this first sector contains the partition tableand another small program that finds the active (bootable)disk partition and then reads the actual bootstrap codefrom that partition, which is then treated like the firstsector of a floppy disk. The partition table processingprecedes the actual bootstrap process, but it must happenin order for the real disk bootstrap to occur.

In the section “Tablesand Routines,” you reference thedevice header in Figure 2 as being 18 bytes. However, inListing 1, the B-byte device name is only initialized to"DRVR - 0 “, or 7 bytes.

In the section “Assembling the Driver,” you decidedto name your handler DRIVER . ASM , which compilesand links to "DRIVER . SY s", a unique name if I ever heardone! Unfortunately, back in the old days when Microsoftand IBM poured the concrete around MS-DOS, someonehad the brainy idea to name the one and only device driverthat anyone would ever need to have, for use on hard andfloppy disks, as-you guessed it-DRIVER. SYS, and notsome more descriptive name like HD. SYS or FD. SYS.

Now here you are with your own device driver and whatdo you call it? Later on you refer to “DRVR” which is atleast a little more unique.

A little later, you warn us to “...keep a system diskhandy” in case the driver code locks the keyboard out. Ofcourse you mean a bootable floppy disk, but some peoplemay not realize this, and this disk needs to have sufficientfiles on it (like a text editor) to allow you to edit the harddrive’s CONFIG.SYS and AUTOEXEC.BAT filestotempo-rarily remove the commands that loaded in the driver andcaused the system to lock up. In addition, if you happen tohave a hard drive configuration that requires a devicedriver to access extended partitions, your safety disk musthave this software on it as well. A safer, and more easilyrecoverable, method is to put your new driver onto abootable floppy disk, insert that disk into drive A, andreboot the computer. This has several benefits, one of





“The ROM bootstrap routines now read the diskboot-strap code from the first sector (the boot sector) of the bootdisk. The bootstrap code is a minimal-services routineresponsible for getting the system up and running. TheROM bootstrap routines check all bootable disk drives forthe presence of a boot sector on the disk. On a hard disksystem with a single floppy disk, the ROM routines firstcheck drive C and then drive A. If no boot sector is found,

an IBM PC transfers control to ROM BASIC and starts upa diskless system; PC compatibles prompt you to insert asystem disk and wait for you to press a key.

“When a bootstrap record is located, the ROM boot-strap loads it into high memory, away from where DOSitself is loaded. Control is then transferred to the diskbootstrap routine.

“After the bootstrap code has been loaded and hascontrol, it looks back to the disk to locate the files IO. SYS

and the MSDOS.SYS.

my mind is not a bad idea. Unlike Mr. Meister, I feel thatmost of you are computer literate readers. I believe you allknow what I mean. As to whether or not one uses the harddisk or a floppy disk environment for driver development,that’s entirely up to you. I don’t write drivers on a dailybasis. I needed to use my Microsoft assembler and itsdebugger. That was installed on my hard disk, not a

floppy*

Chris CiarciaLos Alamos, NM

We Want To Hear from You!

I felt it was sufficient and appropriate within the Write letters of praise, condemnation, or suggestion

article’s goal and context to condense the above descrip- to the editors of C ircuit Cellar INK at:

tion into two sentences. If Mr. Meister feels that this wasinappropriate, I invite him to submit an article detailing Circuit Cellar INK these procedures for us. I personally would enjoy learning Letters to the Editormore about this aspect of the boot phase. 4 Park Street

Now as to the rest of Mr. Meister’s comments, I admit Vernon, C T 06066

that I find myself slightly put off. The fact that I used sevenof the available eight bytes for my device driver name Circuit Cellar BBS: ‘editor”

seems a “nit point.” And “keepinga system disk handy” in 1’ q

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lA/PRODUCTNEVVSNEl/VPRODUCTNEWSNY CONTROLLER BOARD INCLUDES DESIGNOOL FEATURES

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HIGH-RESOLUTIONMAGE CAPTUREBOARD

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Octob er/November 199 1 15





FEATUREARTICLE

Part 1, Wl lbm J. Kressbach

If the edit is to be “clean” andglitch free, it must occur in the shorttime between frames: the vertical in-terval. The vertical interval is the timewhen the TV picture has completedone frame but isn’t quite ready tostart the next. This means that thevertical interval of the incoming sig-nal must be in the same place at thesame time as the signal coming fromthe tape. Fortunately, the VCR doingthe editing is smart enough to do thisfor you. It adjusts the speed of thedrive motor until the vertical synccoming from the tape is synchronous

with the vertical sync from the incom-ing signal.

It’seasytosee thatboth thesourceand destination video must be stable

before a glitch-free edit is possible.While the record deck is responsiblefor ensuring that the “cut in” and the“cut out” edits are clean, it’s still theuser’s responsibility to see that thetape is up to speed and in the right

place for the edit.While limited editing can be done

manually, the precision necessary to

get good edits, every time, where youwant them, requires careful control.

EXAMPLE EDIT

Let’s look at an example. Take thesimple shot sequence given below of ahammer striking a nail.

1. ms (medium shot) hammer poised to strike nail-hammer swings

2. cu (close up) nail as hammer strikes

3. ms hammer raises

To keep it simple, let’s assumethat the source of the picture is a cam-






I I I I I I I I I I I I

I IThe “To Tape” and‘“From Tape” signalsneedaddifionalcondi-Coning between themntrollerandthetape

decks. Since suchcwditioning dependson the tape deck be-ing used. it is impos-

sble lo present a cir-cuit here that would

Figure 1 Ihe video e d t o r co n t ro l le r is ba sed o n mo du les t ha t u se t h e v e ne ra b le Wa g ZB m / c ro c o n t r o lle r .

cost is prohibitive. For that reason,and because it was kind of fun, I de-cided to build my own controller.

My early attempts to build a con-trollerusingdiscretecomponentsanda Radio Shack Model III computermet with some success but it had lim-

ited portability and required a lot ofprocessor time. Often, a VCR wouldgo into a fast rewind and the com-puter, reading the control track on aninterrupt line, would ignore me untilI could stop the VCR manually.

I finally solved the problem ofprocessor time by using a dedicatedcontroller for each VCR. I was alreadyon my third computer and was con-templating my fourth. So, portabilityalso being a factor, communication

through a serial port seemed the wayto go. The ZilogZS controller answeredmost of those needs. While it only hadone serial port, it was available, inex-pensive, and I could afford the cross-assembler I needed to program it.

NAILING DOWN A DESIGN

Figure 1 shows the basic designforthecontroller.It’sprettymuchstan-dard with one exception: I used a 7402

for address decoding. While this is abit unconventional, it allowed me to

20 C IRCUIT CELLAR INK

utilize the extended memory featureof the 28 giving me extra input portswithout adding extra decoding logic.I added a UART for a second serialport, and, of course, I used the ma-chine language version of the 28.

The time code is recorded at 2400

bps. It begins with a marker byte (A5h1,and ends with a checksum. While it’snot compatible with industry stan-dard time code, as long as you don’tneed to use your tapes on a profes-sional reader, it’s not a problem.

The controller does most of theleg work. It time codes the tape andthenreadsitbacktoyou.Itkeepstrackofthecurrent tapeposition,whatmodethe VCR is in (rewind, fast forward,etc.), and conveys user commands to

the VCR. It can search for and find anylocation on a tape and then either playthe tape or wait for a user command. Itcan preview an edit; that is, simulatean edit so that the user can see what itwill look like. It will then perform theedit and review it for you.

There is one controller module foreach of the two editing decks. Theyare daisy-chained through the serialports. Eachmoduleisaddressed sepa-rately and listens in on a party line for

messages designated for it. The mod-ules share a common line back to the

host as well. There are four lines forcommunication: three for the serialI/O, and one for bus arbitration. Acontroller wishing to use thebuspullsthe transistor low, signaling the othermodules that the bus is in use (moreabout this later). The control modules

are designed to have the capacity ofallowing up to 14 modules on oneserial port, but I’ve never tried morethan two. I did this to allow for pos-sible use in automated systems whereseveral VCRs might be necessary. Allcommunicationisfrommodule to hostor from host to module. The modulescannot talk to each other.

Each controller is locked to and isin complete control of the deck towhich it is attached. The parallel ports

of the 28 are able to read the status andremotely control all necessary func-tions of the VCR such as play, rewind,fast forward, cut-in, cut-out, and soon. In general, the same port on the Z8

serves not only to trigger a VCR mode,but to read VCR status as well. Forinstance, configuring port 2 pin 1 forinput reads the status of the VCR’splay LED. Configuring the same pinfor output and then strobing it lowputs the VCR into the play mode. Be-

cause of this, the controller is able tofollow the VCR status even when op-









The Equipment

The VCRs used in this article are Sony 2860As. I have question, and play it. The time readout should count

also used Sony 2850s and tested Sony 5850s with good while the recorded part of the tape is playing, and then

results. VCRs from other manufacturers should work as should stop when the blank part of the tape isencoun-

long as they are designed to work in an editing system tered. Fast-forward the tape a little. The counter should

and are equipped with a parallel port, You should be not move. Now, rewind the tape. The counter should

aware there is no c ompatibility between manufac turers remain unchanged until it encounters the part of the

and you’ll have to check the manuals carefully for pin tape that has been recorded. Again put the tape in

assignments and voltage requirements before attempt- fast-forward, The counter should count until it reaches

ing any interface. Many of the newer VCRs use serial the blank part of the tape, and then stop counting. A

interfaces and may have quite different requirements, machine that reacts in this manner indicates that it is

Many of you may want to try using VHS, S-VHS, 8mm. probably reading from the control track. This makes it a

or other small format VCRs. The c rucial fac tor in a suc- good candidate for computer control. A blank tape

cessful editing interface is the ability to access the control has no control track, so if the readout continues to

track pulses. The pulses must be available not only during count while blank tape is passing over the heads, then

playback, but also while the tape is in fast forward and you can assume that the counter is reading something

rewind. The key to recognizing a suitable VC R is to first other than the control track and the machine is prob-

check to see if it uses a footage counter or a tape time ably unsuitable for conversion.

readout. In the past most consumer VCRs used mechani- Be careful! Each VC R has its own little quirks. For

Cal footage counters for displaying elapsed tape time. instance.1 haveaVCRthatwill notgointorecordmode

This method is much too inaccurate for editing purposes, from play mode; it has to be in pause first. Be sure that

But I have noticed lately that most of the higher end you thoroughly understand the operating characteris-

consumer VC R and nearly all industrial VCRs now display tics of a VCR to be certain itwili fit into an editing system.

tape time in minutesand seconds. They seem to maintain Easy remote control of VCRs with infrared remotes

good accuracy in both rewind and fast forward and it could be achieved through the use of an infrared

seems likely that the control track is being used for tape controller similar to the one described by Steve in

time display. If the manufacturer is using the control track volume 6 of his “Ciarcia’s Circuit Cellar” books.

to display elapsed time, it seems likely that the resource- There are also companies that make computer

ful engineer should be able to find a way to use it as well. interface devices for infrared VCRs. You send them your There is a way to determine if a machine is using the VCR and the c ompany returns it to you with an inter-

control track. First get yourself a blank tape. It must be a face attached directly to the VC Rs infrared sensor. The

tape that has never been recorded on. Record about interface is preprogrammed. ready to plug in to your

thirty seconds of video on it, load it into the machine in computer.

and the cut-out locations. This makesit look like an edit was preformedwithout actually doing it.

If a review has been called for, thecontroller just lets the tape play.

Finally, after a short postroll to letthe viewer see how well the edit fit,the controller stops the machine andthen transmits the exact edit locations

to the host computer.The preroll time, postroll time,and the bottom of the search windoware all user selectable. I should saythat the preroll time changes to fitcertain requirements and VCRs. Thepreroll time for an edit is five seconds.This allows plenty of time for stablepictures before the edit. That is notquite so important for a preview, andso to save time, the preroll for a pre-view is only two seconds.

There are three different editingpatterns that can be selected. Code

Thehost compute randmon i to ra reconnec ted to theed i t ingdecks loca tednearby . Wh i le m an y op erato rs prefe r to use tw o m onitors. I no rma lly use just o ne. Vid eo is sw itche d be tween the two VCR source s au tom at ica l ly . The ed it ing stat ion is loc ate d on a deskwhich is backed b y a b ui lt - in 130-gallon sa lt w a fer aq ua rium . This helps to m a ke the som etim es stressful task of vide o e d it ing a bit m ore relaxing.

24 ClRCUT C ELLAR INK



3Ah selects the “find, play, pause, edit,and postroll” sequence just described.A second similar pattern, 3Bh, adds aslow mode just before the pause. Thisis the one I use most since it pauses thetape a little more accurately. Finally,3Ch has no pause at all. No need topause if the source is a camera.

You can also have the modulefind any location on the tape. Oneversion of this (39h) searches and goes

Figure 4-Finding t he be st wa y to ge t to the

pa use p oint is to e stab l ish a w indo w fo r the

to shoot fo r.

into the play mode when the requestedlocation is found. The other (38h) juststops without going into play. This isin case you’re looking for somethingat the other end of a long tape andwant to refill your Coke while it’s

getting there.Until I started getting this article

ready, I had no idea that the controllerhad become so complex. I developedit over the course of the nine years thatI’ve been free-lancing. I would usu-ally tinker with it when I had work todo but didn’t feel like doing it. Thatmust have happened a lot over theyears.

That covers the construction andsoftware for the control modules. In

part two, I’ll look at software for thehost computer and discuss some op-tions that help simplify the entry andretrieval of editing information. +

Bill Kressbach holds a Master’s degree in In-structional Media and Technology from TheUniversity of Toledo. When he’s not shootingvideos, he does some computer programmingand is chief engineerfora college radio station.

IRS401 Very Useful

402 Moderately Useful403 Not Useful

PARqDlGMThe Model for Programming Productivity

3301 Country Club Road, Suite 2214 l Endwell, NY 13760 l (607) 746-5966 l

Oc tober /November 199 7



FEATUREARTICLEChris ciarcia

Computer Graphicsand the World of Scientific Visualization

As a result of the advance-ments in data generation and com-puter technology over the last fewdecades, methods of managing andanalyzing large volumes of complexdata have been largely responsible for

a strong interest in scientific visual-ization as a new computational tech-nology. This visualization technologyhas its origins within the realms ofapplied science and engineering wheretheuseofcomputerdisplaytechniquesin computer-aided design and engi-neering analysis have provided aninitial driving force for the develop-ment of “computer graphics technolo-gies”duringtheearly 1970sand 1980s.Since then the problem of interpret-

ing, understanding, and processinglarge complex data sets has grownconsiderably. This need has created astrong desire for effective “realistic”graphics tools which have in turnforced these original display tech-niques to expand and grow within avariety of computational environ-ments. As such, a whole new set of“visualization” methods has evolvedbased on the use of computer simula-tions and computer graphics.

Originally, entertainment appli-cations fueled the fires of computergraphics in the middle 1980s whilebasic engineering applica tions becamestandardized and moved out of theresearch context into routine practice.And, the simultaneous developmentof PC technology designed to supportadvanced graphics display capabili-ties served as a foundation and princi-pal support to this evolutionarygrowth process. As a result, the basic

visual vocabulary of computer graph-ics became extended in both breadth

and depth. Graphics applications be-came more adept at meeting the re-quirements of applications needingrealism, visual richness, and motion(animation). Scientific visualizationwas born. Now it seems to be the new

“catch word” and it has become amajor focus of computer graphics inthe 1990s.

Problem Definition

VisualizationEnvironment

ScientificVisualization

Rendering

Figure -The scientific visualization process.

But this emphasis on visualiza-tion technology is an obvious step forthe computational world. As numeri-cal simulation continues to become amoreaccepted (and cost effective) toolfor basic scientific research, the need

of the scientist to understand and “vi-sualize” the complex nature of theirnumerical simulations only increases.Fortunately this process has been en-riched by advances within the enter-tainment world. But regardless of thesource of advancement, computergraphics technology has grown to be-come an essential component of thisnew field of “computational science.”As a result, the current rapid develop-ment in visualization technology

within the sciences and engineeringhas been only impeded by the growthin the power and sophistication ofcomputergraphicshardwareandsoft-ware systems.

In general, “visualization” can bedefined as the use of computer graph-ics imaging technology as a tool forcomprehending data obtained bysimulation, computation, or physicalmeasurement. As such, it is built onthe integration of techniques

“snatched” from older technologiesincluding computer graphics, imageprocessing, computer vision, com-puter-aided design, geometric mod-eling, approximation theory, percep-tual psychology, and user interfacestudies. But the most fundamentaldefinition of the visualization tech-nique lies not in its components butrather in its intent. It is important toremember that the purpose of scien-tific visualization is to gain “insight”

into the behavior of some complexprocess under scrutiny. Individual

26 ClRC LJlT C ELLAR INK



numbers (or single components of aarge database) are not important. In-tead, its effectiveness lies in its abilityo rapidly communicate large amounts

of information in a format that en-hances comprehension and insight.

Historically the concept of visual-zation predates the computer era. If

you think about it, visualization hasbeen a part of the scientific methodever since the Greeks. They employedbasic linear graphing techniques inheir complex architectural designs.

But now we seem to want to handlemore than one-dimensional data, andhis new “complexity” requires that

we be more creative in our renderingechnique.

Therefore, in order to explore thesevisualization concepts on a practical

evel, I’ve decided to center this articleabout a detailed description of how tostructure and implement a basic “vi-sualization process” like thatflowcharted in Figure 1. I propose thatwe develop a computational “visual-aid” that will utilizenumericallysimu-ated data from the application of

Newtonian mechanics to the motionof an object within a gravitational fieldn order to demonstrate how basicnsight into a system’s behavior can be

gained from this visualization pro-cess. In doing this, we will be calledupon to apply basic tools from nu-merical analysis, computer graphics,and animation.

THE VISUALIZATION PROCESS

The best example is one that canbe easily recognized and compared toone within our own personal experi-ence. I have therefore chosen to “visu-

alize” a system based on the motion of a ball, falling off a wall and bouncingnto a hole. It’s a simple system that

each of us can visualize from experi-ence. As such, it will be easy to “see” if our numerical modeling and visual-zation look and act like the real thing.

But don’t be fooled. A simpleexampledoesn’t guarantee a simple computer model. A true representation of thisprocess requires that we numericallysolve a secondorder differential equa-

ion, create a visual environment, andanimate a time-evolving process.

We will construct this “scientificvisualization” along the guidelinesshown in the flowchart in Figure 1,where

1. Problem Definition-The basic problem is defined and the nature of the physical system to be visualized isdetailed. This process includes the

definition of the type of process under study, the limits on its behavior andits environment, and the underlyingscientific principles involved.

2. Modeling ~mafhemafica&--Thesystem model is chosen. Since thisexample will involve the application

and the configuration of the displayvehicle.

4. Creating the Visualization Envi-ronmenf-The background and eachcomponent of the visual display isdefined in detail and constructed for use within the “active” visual mode.This step involves the actual coding of

each component and the setup of anyanimation requirements.5. Rendering-Each component of

the “scientific visualization” applica-tion is combined to create an inte-grated environment. As the procedureisrun,themathematicalmodelisused

Ball

AY

Ground

Figure 2-The example used in the a rtic le is a simple ball which falls off a w a l l bounc es, and

usua lly fa lls into a ho le ne a r the righ t side of th e system .

of physical laws of motion, the math-ematical technique to be used must bedefined and applied in order to deriveappropriate equations of motion.These need to be consistent with a

form that is easily used within thecomputer graphics display environ-ment.

3. Visualization Mapping-The na-ture and extent of the actual “visual”display is defined, that is: What is theviewing field? How many objects willit contain? What form of backgroundis necessary? What video mode andresolution is necessary? Do you use black and white or color? Is the sceneanimated? In other words, this step in

the visualization process requires thedefinition of all the basic components

to predict the behavior of the systemin a step-by-step manner. The visualdisplay is then upgraded in a continu-ous fashion to reflect the changes inthe mathematically derived data.

Of course the specific procedureshown above is not “universal” to allscientific visualization processes. Thesource of our data could have beenempirical or from a closed-form ana-lytic solution instead of our chosennumerically simulated data. And thenature of the problem itself will obvi-ously change with application. How-ever, the techniques and conceptsemployed are generic across the spec-trum of physical science and can be

readily applied to many differentfields.




Our goal within this article is to gothrough the flowchart in Figure 1 in astep-by-step fashion while flushingout each component in order to createa practical, working scientific visual-ization example. But since this or anyother example is highly dependent onthe programming language, graphics

library, and display deviceused, I havechosen to develop our example in as“generic” a fashion as

possible. For a program-ming language I havechosen FORTRAN. Thisis n o t b e c a u s e Cwouldn’t be better. It’s

because I find FOR-TRAN easier for peopleto read. They can usu-ally follow the program

flow better without be-coming programmingexperts. Most of the timeI use C, but this is only

because I get better ac-cess to system-level func-tions for enhancing mydisplays. However, inthis application that isnot necessary.

PROBLEM DEFINITION

The first step in the example is thedefinition of the exact nature of the

problem we are going to solve. Wewill consider the motion of a bounc-ing ball that first rolls along the top of a wall and then falls off and bounces

several times until it falls into a hole inthe ground. A drawing of the appro-

yn +k 9

we will neglect air drag effects in this problem. But because the ball impactswith the ground and loses some en-ergy through that interaction and inthe elastic deformation process of the

ball’s surface, it is known that thevertical velocity is not conserved after each bounce. We can make a good

approximation to our own observedreal-world action by assuming that

approximately 28% of the total kinetic energyis lost during the ball-ground interaction. Thisis reflected in a verticalvelocity damping of about 15%aftereachcol-lision with the ground.Theverticalvelocity(Vv1of the ball after each

bounce is therefore approximately equal to thenegative value of 85% of the vertical velocity be-fore the bounce.

yn

For a graphics library I have chosen to

use the Microsoft Graph-icsLibrary Routinescon-tained in the MicrosoftFORTRAN V5.0 distri-

bution. Microsoft seemsto a fairly universal stan-dard and available to

t n+d? l

Figure3-The Runge-Kutta procedure uses a w eighted average of slop e s,w i t h those in the c enter rec e iv ing tw ice as muc h w eigh t as those o n the

As a “study” vari-able in the system, wewill allow changes in theinput of the magnitudeof the constant horizon-tal velocity Vxo. For our

purposes here, this value

will range from 0.38 ft/set (when the ball bounces and then justrolls into the hole) toabout 4.7 ft/sec wherethe ball has sufficient ve-locity to be “dunked”

most programmers. It is not the mostideal graphics set, but it does containmost of the basic graphics utilitiesneeded for addressing and assigningvalues to individual pixels within the

display screen. Its most obvious fail-ing lies in its restriction to the stan-dard VGA modes. The best it canhandle with 256 colors is the 320 x 200display resolution. Of course you canimprove the resolution to 640 x 480 if you wish to be restricted to 16 colors,

but I usually find this unacceptable. Ilike maximum “realism” wherever

possible. If you are looking for a morecomprehensive graphics library todevelop your own visualization application under, I recommend the Ge-nus GX Graphics Toolkit.

priategeometryanditsassignedcoor-

dinate system is shown in Figure 2.The ball will start its motion at the

coordinates (Xo,Yo) = (-1.0, 0.8) androll horizontally at constant velocity

Vxo until it reaches the edge of thewall f-0.8,0.8). It will then fall off thewall and strike the ground 1.3 feet

below and bounce upward. Theground itself is defined to be 0.5 feet

below the coordinate axis (y = -0.5).Each time the ball strikes the ground itwill either bounce or, if it falls in theappropriate place, it will fall into theholeandbetrapped.Thisholeisplaced

1.25 feet from the base of the wall. It is0.3 feet deep and 0.10 feet wide.

The ball is assumed to move hori-zontally with a constant velocity since

into theholewithoutbouncing. Higher velocities will miss the hole entirely.Several choices of Vxo are possiblewithin this range which will cause the

ball to land in the hole after a series of

bounces. If the ball misses the hole, wewill continue the computation until itreaches a horizontal coordinate loca-tion of 0.85 feet (Xstp>. If it enters thehole, we will allow it to slide down-warduntilitfalls toacoordinatedepthof Ysfp = -0.8 feet.

Since we will be studying the“motion” of a “dynamic system,” wewill be solving for the coordinates of the ball in a point-to-point fashionduring the time of its motion (flight path) from the top of the wall until itstops. The best visual aid for this ex-







ditionsand decisioncoordinates. Sincea high degree of accuracy is not re-quired, each of these variables can bedefined as REAL*J in our example.The integer counter i is defined asINTEGER* 2 since we expect to exceed127 df time steps. See Listing la.

The initial horizontal velocity is

then input and the loop variables (x,y, Vv, i, time, Xin) are set to theirinitialconditions,showninListinglb.

below it (based on the distanced trav-eled in one time step dT), then wemust determine if it is falling into thehole or not. This is accomplished bytesting to see if the x-position is withinthe hole’s width between x = 0.45 to x= 0.55. If it is, then the position is resetto the center of the hole (xin) and the

ball is drawn at the new position andallowed to fall to the bottom in thenext few cycles.

The cycle counter is thenincremented by 1 and the basic loopprocedure is started. Since this is an“animation sequence,” the last draw-ing of the ball within the display im-age is erased so that the new imageposition can be drawn after its newposition is determined. However, be-fore this calculation takes place, the

current position and velocity corre-sponding to this last (ith) cycle isstored in temporary storage Xold,

Yo Id, Vvo Id) and the new x position(for cycle i+l is determined. If the ballcollides with the ground, these previ-ous (old) values will be used to deter-mine the ball’s reflection from thatsurface. If the ball is still on top of thewall, that is, for x less than xe, then theball is drawn at its new horizontalposition and the counter is incre-

mented for the next cycle. Otherwise,the i+l cycle y coordinate y , verticalvelocity WV), and the total elapsedtime is calculated. See Listing lc.

Thiscentercoordinatexinisusedfor multiple purposes. It centers andconstrains the motion of the ball as itslides down the hole so that we cansimulate the realistic motion of a solidspherical ball sliding down a circularpipe slightly larger than itsown diam-eter. But at the same time it is used asa trigger function. It indicates whether

or not the ball has entered the hole. IfXin = 0 then we know that the ball hasyet to reach the hole. If Xin is greaterthan zero then we know it has just hitthe hole or is sliding down it.

Once the new position of the ballis determined, it is necessary to makeseveral conditional tests to determinethe current status of the calculationsequence. The position is first testedto determine if the ball has reached itsend-point boundary conditions. Inother words, has it fallen into the hole

and reached itsbottom (Ystp = -0.80)or has it bounced past the hole to theright-hand side of the display screenand reached the x-stopping point(xs tp = 0.85)? If either of these condi-tions is met, the calculation and ani-mation sequence is suspended.

If the ball is not in the hole and they coordinate indicates that it has col-lided with the surface, then the ballmust bounce. Under these conditions,the new x-coordinate location andvertical velocity are calculated usingthe previously stored values from the

last cycle. The velocity is thendampedby 15% and its direction is inverted tosimulate the reflection of the ball offthe ground surface. The new positionof the ball is then displayed in theanimationsequenceand thenextcycleis initiated, as shown in Listing Id.

Once the total motion sequence iscompleted, a new horizontal velocitycan then be input and a new test of theball’smotioncanbe “visualized.“Howthis visualization is accomplished us-

ing the simple graphics utilities avail-able within the Microsoft GraphicsUtility Library is the subject of thenext few sections.

VlSUALlZATlON MAPPING

If the ball has not reached these The next step in creating a work-stopping boundaries, we must deter- able “visual” representation of ourmine if it should bounce or continue in scientific model is based on the defini-its upward or downward flight path. tionofthegraphicsenvironment.ThisThis is accomplished by testing the display must be chosen carefully since

value of the y coordinate. If the ball’s it is highly dependent on the nature oflocation is at the surface or slightly the process being visualized. For our

October/November 199 1 3 1



bouncing ball scenario, we need onlyconsider the animated motion of asingle object: the ball. But that ballmust move within some referencedenvironment. This environment, orbackground image, must be laid outto correspond to the system limits andboundary conditions specified in the

previous “modeling” section. Andsince this is an animated visualiza-tion, we must take into account thespecific hardware used. This greatlyaffects the time needed for imagemodifications. It’sobvious thatdiffer-ent graphics cards, screen memorymanagement, and processor clocksspeeds affect the rate at which a pixelon the screen can be changed. There-fore, before selecting the display mode,the following should be considered:

1. How much visual detail doeseach object or component of the back-ground require?

2. How many colors or shades ofgray are necessary to properly renderthat detail?

3. If you are animating objects,what constraints on the image refresh

Figure 5a A Iwo-d imens iona l textured ba ckground is used to ad d some rea lism to the

simu la t i on .

speed exist due to the size and num- 4. What constraints do you haveber of colors of each object (the num- placed on your choice of video modeber of bytes per pixel and the number resultingfromcompatibilityandtrans-of total pixels within an object affect portability to other PCs?perception of the motion since the I’m sure you can think of othervideo refresh rate is not variable)? important questions that you would

dh

ala warsion SUppOrMTurbo C, Microsoft C,QuickC QuickBASIC

and Turbo Pascal.

R e a d e r s e r v i c e 1103

32 C lRCUlT C ELLAR INK



Figure5b-A block-line background is often used due to its simplicity, but fails to add

any realism to the system.

How you choose this background

ask during a design review, but I think

can make or break the visualization.

the four listed above give you an ideaof the type of thought that goes into

Perception is a funny thing. It is highly

choosing the “visualization map.” Forthis article I was highly constrained

dependent on context, especially

by Question 4. If this example is to beworked with by most of you, I needed

where motion is concerned. I there-

to keep my graphics mode to a widelyaccepted standard. This meant choos-

fore chose to create our example back-

ing between standard EGA or VGA

modes. And since all computer sys-tems with a VGA card support thebasic 320 x 200 by 256-color mode, Ichose that for this exercise. My choiceof the 256-color mode was based onmy desire for some realism. I wantedto generate a black-and-white (B/W)display but I didn’t want to be limitedto the four shades of gray that thestandard 16-color modes of EGA orVGA would allow. By selecting the256color mode, I could then construct

a B/W table of 64 shades. This wouldallow me to render the wall and ballwith some detail. Also, as long as Ikept the size of my ball down, I couldrender it as a 3-D object instead of a l-D point or a 2-D filled circle. This atleast would add some realism to thevisualization.

ground using a textured surface forthe wall and ground. This tended tomake the eye see this ball as bouncingon a piece of concrete viewed fromface-on, as shown in Figure 5a. Thetexture lends some 3-D effect to thesurface of the wall and ground. Thiscompensates for the “flat-look” expe-rienced when using the more tradi-tional line, solid-fill-rectangle mode

of drawing (see Figure 5b).

CREATING THEVlSUALlZATlONENVIRONMENT

Every program using the graph-ics library must explicitly declare anyroutine it uses. This means that youare required to reference the interface

routines provided in the include filesFGFCAPH FI and FGRAPH.FD which

With the display mode and basiccomponents chosen, eachof the visualconstructs must be coded in our de-velopment language. This is accom-plished through the use of a variety ofgraphics utilities provided within theMicrosoft run-time library

GRAPHICS.LIB) which are linkedtogether when the executable is cre-ated. However, the steps necessaryfor this “environment generation”process must be accomplished in spe-cific correlated steps which build onone another to create the desired vi-sual display effect.

contain all the procedure declarations,structure, and symbolic constant dec-larations for each of the called graph-ics functions. These should be the firsttwo lines of code in your program.

SElTlNG THE VIDEO MODE

The display device utilized by therunning computer system must firstbe polled to determine if it is capableof supporting the chosen video mode.If it is, then the mode is set. Otherwisethe execution of the example visual-ization is terminated.

An example of the FORTRANcode needed to implement this step isshown in Listing 2a. Thegetvideoconfigprocedureisusedto find the type of video adapter that is

installed. This information is returnedin the /videoconf ig/ structure de-fined in FGRAPH . FD and referencedwithin our code through the record

declaration. The actual video mode isset by a call to the setvideomodeutility and passing it theSMRES 2 5 ~COLOR parameter request-ing that the video modebe set to VGA320 x 200 by 256 color. The integervariable dummy is used to return er-ror/success flags. If setvideomode

sets dummy to zero, the hardware re-quested is not available. This condi-tion is tested. If dummy is set to anonzero number, this indicates thatthe video mode was successfully set.

SElTlNG THE COLOR PALEllE

The selected VGA video modeenables us to use up to 256 colors atany one time within our scientific vi-sualization display. This grouping of

allowed colors is defined as the dis-play palette. If we had chosen someother video mode, we could have pal-ettes containing 2, 4, 8, or 16 colors.Each of the colors in a palette is refer-enced by its respective “index num-ber.” In the VGA 256-color mode, wecan mix varying amounts of the basecolors red (RI, green (G), and blue (B)to create up to 262,144 (256K) differentcolor combinations. Two-hundredfifty-six of these can in turn be as-

signed for use within our application’scolor palette.














FEATURE

ART’CLEAdd a Video Display to

Larry Duar te

Your 803 1 Microcontroller

G ra p h ic s a nd C o lo r Liven Up An y Outp u t

I J

I n many control ap-

plications, it is often nec-

essary to display informa-

tion of some form for hu-

man consumption. Most

solutions have centered

on one- or two-line LCD

displays because of their

small size and low cost.

However, with the rightinterface, it is almost as

easy and inexpensive to

design into your circuit

an 80-character by 25

line or 40-character by

25line video displaywhich uses either mono-

chrome or color. Video

displays give you much

more room to display text

and graphic information,

and color livens up any

screen.

40 ClRCUlT C ELLAR INK

The design I present here can beused with most basic 8031-based cir-cuits, and requires minimal softwareand hardware overhead. Since 8031-

type circuits have been presentedmany times in the past within the

pages of this magazine, I’m only in-cluding those portions of the 8031 cir-cuit necessary to clarify thediscussion(see Figure la). The video interfacecould also be adapted to other proces-sors with a few changes.

THE NCR 72681 CGMA

The heart of the video interface is NCR’s 72C81 CGMA (Color Graphicsand Monochrome Adapter). There are

lower priced alternatives, but its fea-tures and level of integration made it

our choice. The chip includes full compatibility with IBM CGA and MDA,Hercules, and high-definition CGA. Ithas an internal 6845 and character-generator ROM, and requires just twoRAM chips and a clock to be fully

functional. In this article, the 72C81 isconfigured for monochromeCGA; thatgives us the ability to switch between80-column and 40-column modes,which is very useful for small moni-tors.

The 72C81 comes in an 84-pinPLCC package. The pinout is shownin the schematic in Figure lb.

ADDRESS DECODING

The 72C81 was intended for use inIBM-compatible display adapters, and

Add ing a v ideo display interface t o yourm icrontrol ler d esig n is straight forwa rd to d o u sing NCR’s 7 2 C 8 1 CGMA c h ip a n d a l lows the use of g rap hic s an d c olor to q uic k ly im prove a ny user interface.



as such uses standard CGA addressesfor its I/O ports and video buffer andincludes 20 bits of address input. The8031 does not support separate I/Oand memory addressing, but doessupport two separate 64K areas knownas Code space and Data space. In mysetup, the system EPROM is mapped

in Code space (selected by *PSEN)while RAM and I/O share Data space(selected by *RD and *WR).

“Glue logic” wasnecessary to con-vert between the reduced 8031 ad-dress space and the much larger 72C81space. In Figure 1, the 74LS138 breaksup the 8031’s Data space into eightblocks of 8K each. The fourth block-24K to 32K-is reserved for I/Oaddressing. Reads from or writes tothis area generate *IOR and *IOW

through the 74LS32. The bottom 2K ofthe I/O block is further broken up bythe 74LS154 into 16 blocks of 128 ad-dresses each. A memory map for thissample system is shown in Figure 2.

The 74LS244s are used to movethe 72C81 I/O port addresses out ofthe lower RAM area and adapt the8031 16-bit address to the 20-bit ad-dress bus of the 72C81. They performthe following translation:

Video BufferI/O Ports

80318000-BOO063D4-63DC

Video Buffer73C81

B8000-BBOOOI/O Ports 3D4-3DC

Thus, to display information youonly have to write to Data space be-tween addresses 8000h and BOOOh. Todeal with the display’s control regis-

ters, write to addressesbetween63D4hand 63DCh. Dealing with the display’scontrol registers is the same as dealingwith a standard IBM PC CGA board,so I won’t go into that here. There areplenty of excellent references avail-able that describe the CGA in detail.

THE MISSING WAIT STATE

While documentation NCR pro-vides for the 72C81 is very good, it

fails to adequately stress the fact thatthe IORDY output must be hooked up

Figure 1 a-Since 803 l-type c irc uits have be en presented m any time s in the p ast, only

those portions of the sc hematic nec essary to c larify the d isc ussion are shown he re.

for the chip to operate properly. The to stop the processor clock without72C81’s internal 6845 places a high losing the registers. We also don’t usepriority on displaying RAM (so that the internal oscillator circuit of thethe CGA’s famous “snow” doesn’t CPU. Instead, a clock is generated ex-flurry across the screen) and some- ternally (in our case using a 7404) and

times has to delay writes to the video is used to drive a 74LS74 and a 74LS32.buffer. Since the 8031 doesn’t have While the IORDY line is low, the clockany kind of “wait” or “ready” input, is passed through to the processor.connecting IORDY presents some- When IORDY line goes high, the clockthing of a problem. If we ignore is shut off, stopping the processor inIORDY, we’ll likely lose information its tracks until the video processor isthat was sent to the display, but ig- ready to continue. The 74LS74 guar-nored by the 72C81 since it was busy antees that turning the clock on anddoing other things. off is synchronized.

The solution involves using theCMOS 8OC51 or 8OC31. These chipsuse static memory for theinternal CPU

registers, rather than dynamic as inmost NMOS processors, allowing us

SOFIWARE

Listing 1 shows a very simple in-terface to the video display. Its main

October/November W I 4



Figure 1 b-The hea rt of the d ispla y interfac e is the NCR 72C8 1 CGMA c hip. Whiie intended to b e used to m ake grap hics bo ards for IBM

PC-c om pa tible c om puters, it is r e a d / y ad ap ted for use by ma ny emb edd ed m icroc ontrol lers.

O Map

Code Space 64~ 64~ Date Space

Program ROM

1408

1290

1152

1024

896

708640

512

384

256

128

24K 0

1012

I011

1010

109

108

107106

105

104

103

102

101

46K

27512WW video

RAM

Or . 32K 32K

video uo

24K

27256(32~)

16K

P ram“8 RY

OK OK

Plus 256 Bytes Internal RAM

Figure 2--The 805 I s ad dress spa ce is broken into two regions: read -only Cod e spac e and read/ write Data spac e.

42 CiRCUlT CEf LAR NK

purpose is to initialize the display and

write “Hello, world” to the screen. It iswritten in C and can be compiled toROMable code using the Franklin Ccross-compiler for the 8031 (or anyoneelse’s compiler with some minor modi-fications to the source). A few addi-tions to this code should make it use-ful for any application.

CONCLUSION

The circuit board components can be purchased for about $35.00. For control applications, a small 5-inch to9-inch monochrome monitor (color frequency, 12-volt supply1 can be

bought for $25.OOfromsurplus houses.

The ability to add a video displaywill be useful for many 8031 projects.

NCR also has a similar chip that supports VGA graphics. The NCR 77C22

supports the standard VGA modeswhile providing enhancedmodes such











Handset

Analog AudioSpeaker/

Microphones Interface

_ Gain ControlBlocks &Programmable

b Filters

---) Codec(p or A law)

---) Serial TDMHighway Interface

Dx

_Dr

T I T

Figure 2-A simp lified bloc k d iagram of the AT&T V540 digital telephone CODEC.

section. This circuit is connected tothe T7250B line transceiver section.The physical interface for ISDN basicaccess is provided via an &position

RJ-45 modular jack.5. PC Bus Znferface Circuitry. The

BRI adapter board is mapped into theI/O space of the PC with address lo-cations ranging from 200h to 3FFh.Data bus buffering between the localbus and the PC bus is provided by abidirectional bus transceiver. Addressdecoding for chip selects and devicecontrol signals are also provided inthis section.

VOICE PORT WITH SPEAKERPHONEFUNCTIONALITY

The AT&T T7540 digital tele-phone CODEC (Figure 2) providesthe flexibility needed to support a va-riety of analog voice ports. Audiofunctions include a CODEC-filter fea-turing CL/ A-Law companding. Addi-tional voice port functions includeprogrammable touch-tone (DTMF)generation and ringer tone genera-

tion. The device also contains a pro-grammable sidetone insertion inter-face. The T7540 is controlled via anexternal microprocessor.

The T7540 has a serial interfacefor digitized voice, a parallel inter-face for microprocessor control, andthree pairs of differential analog au-dio interfaces to the handset, hands-free speakerphone, and auxiliaryequipment such as answering ma-chines or alerters.

The serial KM interface for digi-tized voice is a fullduplex serial time-

division-multiplexed bus. This serialhighway is programmable and ac-cepts variable data rate clocks rang-ing in frequency from 64 kHz to 4.096

MHz. The serial highway interfaceconnects directly to most PCM buses.In our design, the KM interface con-nects directly to the T725OB ISDN Sinterface chip. The parallel micropro-cessor interface of the T7540 is flex-ible and is interfaced easily with Intelor Motorola microprocessors. In ouradapter board design, the PC micro-processor (80x86) controls the trans-fer of information in and out of theprogrammable internal registers of

the T7540.The three analog audio interfaces

of the T7540 are the handset, hands-free, and auxiliary interfaces. Each ofthese interfaces consists of a differen-tial input and a differential output.The handset and auxiliary outputs candrive a 300-Q load directly and areprogrammable from +0 to -23.25 dBin increments of 0.75 dB. The speakeroutput can drive a 50-Q speaker di-rectly and is adjustable over a 69-dB

range in 1.5-dB steps.The T7540 provides the function-

ality needed to support microproces-sor-controlled hands-free speaker-phone operation. The microprocessormonitors and controls the system insuch a way that the coupling fromthe speaker to the microphone andpoor hybrid matching does not resultin oscillations, ringing, or unpleasantechoes.

The T7540 provides signal moni-

toring of the transmit and receivepaths. Received signals may be ex-

amined over the entire channel band-width or an 800-Hz second-orderhigh-pass filter can be selected. Speechtends to have a large part of its en-

ergy above 800 Hz, whereas roomnoise has a significant part of its en-ergy below 800 Hz. Selecting the 800-Hz high-pass filter will reduce theneed for gain switching due to noise.

To reduce the amount of micro-processor overhead required to moni-tor the voice signals, maximum-valueregisters are provided on the T7540to obtain an envelope of the receivedand transmitted voice signals. Thesemaximum-value registers retain the

highest value of the, received signalsince the last register read was per-formed. The maximum-value methodcan provide a reasonable representa-tion of the signals for a period of sev-eral milliseconds. The time requiredbetween register reads depends onthe hands-free algorithm developedby the user. Figure 3 shows how theT7540 is wired on the BRI adapterboard.

DATAPORT INTERFACE

Data transfer on the ISDN B2channel is supported by the T7121. Itconnects the serial communicationlink carrying High-level Data LinkControl (HDLC) bit-synchronous dataframes to the host PC. There is anoptional transparent mode of opera-tion in which no HDLC processing isperformed, allowing the use of otherprotocols (Figure 4). The T7121 com-

municates with the PC as an I/O-mapped peripheral and is controlled

October/November 199 J 47















Data Call

KeyboardConversation File Transfer

Operating System Application Interface Utilities C Language

ISDN“Tr’ StateManager

INFOstateControl

Layer 3 Modu le

Call Reference Control,Packet Format Control,Layer ‘YLayer 2 Control

Layer 2 LAPDModule

Frame Buffer Queueing,Flow Control

Layer 1 Voice Port Data Port SignalingPort D e v i c eDrivers

T7121 T725OB

Bl 82I

D

I ISDN BRI Line

Figure 11 -Ge neral structure o f the software e nvironm ent.

LAPDFrame

Octet 2

Octet 3

Flag Address Control Information CR C Flag

Octet 2 is transmitted first; within each octet,the least-significant bit (LSB) is the first bit

Figure 12--7he bit fields of an LfJAD frame contain c omp l e t e ad dress, control, and da ta n

f o rmat ionp lusCRCer ro r check -

i ng.

SAPI=Service Access Point Identifier TEI = Terminal Endpoint Identifier C/R = Command/Response BitEA = Extension Address (O=extend; I= Final)

nI?.

6

October /November 199 I 55



the protocol control diagrams of theQ.931 standard. Each subblock istreated as an independent task underthe control of the application programinterface and TE state manager. Thefunctional signaling supported in theLayer 3 module has been tailored forthe services offered by the AT&T 5ESS

central office switch. Layer 3 softwareto support new supplementary ser-vices or to support other central of-fice switches requires some custom-ization. Such customization is avail-able from third-party vendors suchas Link Technology, Holland, Pa., andDGM&S, Mt. Laurel, NJ. Since oursoftware was very coarse and onlyserved to test our design, we feel itwould cause more problems than itwould solve to release it.

INTEGRATED VOICE/DATA ADAPTERBOARD SUMMARY

The ISDN adapter board designoutlined here provides a low-cost,high-performance terminal endpoint.This board allows users to simulta-neously access both voice and dataservices of an ISDN BRI line at the Sor T reference point. The PC plug-inboard can operate in any IBM-com-patible computer using the industry-standard architecture (ISA).

A four-layer printed circuit boardwith the functionality outlined in thisarticle has been prototyped andtested. The adapter board design pro-vides the audio functionality neededin a digital telephone or an integratedvoice-data workstation. Software run-ning on this hardware platform sup-ports not only the Layer 1 “devicedrivers” but also the CCITT standards1.441tQ.921) and 1.451(Q.931) for Lay-ers 2 and 3. The user interface is viawindow-driven menu options whichare very flexible and easy to use. Thisboard allows users to quickly learnabout the T7540 digital telephoneCODEC providing speakerphonefunctionality, the T725OB ISDN BasicRate Interface “s” transceiver, and theT7121 HDLC formatter.

For additional information anddocumentation on the devices out-lined in this article, contact AT&T Mi-croelectronics at (800) 372-2447. $P

56 ClRCUll CEl LA R INK

Steven Strauss is a licensed Professional Engi-neerandamemberoffhetechnicalstaffat

AT&T Bell Laboratories in Allentozun, Pa.,specializing in communications devices. Heholds a B.S.E.E. from Pennsylvania StateUniversity and an M.S.EE from Rensselaer Polytechnic Institute in Troy, N.Y.

P.K. Govind is a distinguished member of the

technical staff at AT&T Bell Laboratories in Allentown, Pa. He is an application wnsult-ant for communication a evices and has exten-siue experience in product planning, systemintegration, and product akvelopment. Mr.Govind received an M.S. and Ph.D. in physics

from the Unimsity of Colorado, Boula r,Colo.

REFERENCES

1. T7540 Preliminary Data Sheet,D X9-148SMOS. AT&T Micro-electronics, 1991.

2. T725OB Advance Data Sheet,DS89083SMOS. AT&T Micro-electronics, 1989.

3. T7121 Data Sheet, DS90-

087SMOS. AT&TMlcroelectfon-Its. 1990.

IRS4 10 Very Useful411 Moderately Useful412 Not Useful







I.4

c l4

OrCAD Schematic Design ToolsA Wo rking Eng ine e r’s Im p ression

b y Bruc e Web b

Schematic Capture with Schemab y Ken Da vid son




SPECIALSECTIONBmce Webb

OrCADSchematic Design ToolsA Wo rking Eng ine e r’ s Im p re ssio n

L ike a lot of people, I stuffed making

printed circuifs with dr f t ing tape nd

“rub-on” pads. Not content with such crude techniques, I started investigating what

w s available to computer ize the process.

So, f ive years go I tr ied using a general-

purposeCADprogrum.

Then I got a printed circuit layout

program (Tango from Accell Tech-nologies). Last year my companybought an autorouter and schematiccapture software. Each upgrade madethe job a little easier, a little faster, andmore accurate. The last improvementturned out to be the most profound.Getting the schematic into the com-puter makes a big difference.

The process of printed circuit lay-out involves four basic steps:

1) Design the circuit (draw sche-matic)

2) Place parts on board3) Route connections (manual

and/or auto)4) Check board against schematicSchematic capture programs per-

form or assist with three of the four:designing, routing, and checking. Thehardest part for me has always beenmaking sure that the printed circuitmatches the schematic before I spendthe timeand money fabricatingboards.That is where schematic capture makesa big contribution.

60 CIRCUIT CELLAR INK

ORCAD

OrCAD Schematic Design Tools(SDT) is a low-cost schematic captureprogram which may be used withother design products as part of acomplete printed circuit design pack-age or alone to create standard andeasy to read schematic diagrams.

OrCAD SDT is not a single pro-gram; it is a collection of programs (or“tools”) that provides a way for theuser to create, edit, check, and printschematics. It requires a minimum offive megabytes of hard disk space onan IBM-compatible computer with atleast EGA graphics, 640K or more ofRAM (EMS supported), and a mouse.The results of your efforts may beprinted on most popular printers oron an HP-compatible plotter. I use a16-MHz80286machinewith4Mbytesof RAM, a super VGA display, and anHP-compatible laser printer. I useTangoPCB and autorouter to createPC board layouts from OrCAD netlists.

The heart of the OrCAD SDT soft-ware is a drawing program calledDRAFT. DRAFT starts with a blankdrawing sheet that includes a titleblock where company name, sche-

matic title, revision date, and so on arestored. The title block is not just anarea on the drawing; it is a kind ofheader that makes it easy to keep trackof your documents. A pull-down win-dow provides access to the DRAFT

commands. The operation is intuitive,though some time with the manualmay keep the user from confusingcommands.

DRAWING FEATURES

Drawing a schematic is as simpleas retrieving the parts that make upthe design from libraries and connect-ing them with lines or “wires” on thescreen. OrCAD also allows groups ofwires to be collected into buses tomore easily get the connections fromone area of the schematic to anotherwithout cluttering. Special connectionssuch as power or ground are made tonodes which are implicitly connected.The process elements are pretty muchthe same as hand drawing, except thelines stay straight without a ruler.

Large schematics may be dividedinto sheets with either a flat or hierar-chical structure. Connectionsbetweensheets are accomplished using mod-ule ports. The flat structure has thesame level of detail on all sheets. In ahierarchical structure, the detailedlower levels of the drawing are repre-sented as blocks at levels nearer thetop.OrCADSDTallowsblocksofsche-matics which are repeated in the de-



signtobeshownonceonasingle sheetand then referred to by a block desig-nation. The more complex your sche-matic, the more you will appreciatethe completeness and flexibility ofthese structures. Fortunately, if yourneeds are simpler, these options donot get in the way.

LIBRARIES

Only the libraries you use need tobe installed. There is no point in hav-ing OrCAD search through digitalcomponents if your design will onlyuse analog parts. Components not

Schematic versions of electricalcomponents are stored in SDT’s ex-

available in OrCAD libraries can be

tensive libraries of more than 20,000parts. The components are rectangles

made from existing parts or built from

or logic shapes with the “pins” repre-sented as lines. Each pin is labeled

scratch. I have created, for example, a

with its function name. Using libraryparts relieves the user from the effort

complete library of my own of Maxim

of redrawing them, and since the li-

braries have been debugged by years

interface and microprocessor control

of use, it is unlikely that you’ll en-counter any mislabeled or missing

components that OrCAD didn’t in-

pins. The libraries are organized byfamilies such as CMOS, ‘ITL, or ana-

clude. I also created special RAM/

log, and by manufacturer such asMotorola or Intel.

ROM chips for designs where either

SCHEMATIC CAPTURE SOFFWARE EECAD)

an EPROM or static RAM (like 2764 or6264) can be installed.

One of the hardest skills I havelearned in drawing schematics is pre-dictinghowmuchspacewillbeneededbetween components for wires to run.Moving a part to another area on theschematiccanbedonesothatthewires

move with it, but the results are usu-ally messy and have to be redone more

pins wired to a third could be con-nected together directly. Power andground lines are generally tied tonodes which are implicitly connectedto keep the drawing less cluttered.

The net list provides a way tocommunicate the schematic connec-tions to a PCB layout program. All of

the connections are then routed eitherby hand or using an autorouter. I pre-

OCAD b oa sts 50,000 users and ha ve de velop ed suppo t f

for them that I found to b e reasona ble a nd c lear . The re

has alwa ys be en som eo ne a t the other end when I ca t t ed

and if the person I first rea c hed c ouldn ’ t help, I wa s c a lled

ba c k w ithin a few hours with the a nswe rs.

than once. I usually try to completesmall blocks of schematic and place

A schematic capture program

them rather than placing individualparts. This is also a good idea when

helps you to draw an easy-to-read and

placing parts on the PC layout. Youhave a schematic. Now what?

somewhat standard drawing, but thereal magic is what happens once theschematic is complete. The schematic

can be used to create a file of thedrawing’sconnectionscalled a net list.The net list is an ASCII listing of all ofthe wires on the schematic with theendpoints of each being a componentpin. The connections are grouped to-gether into nets. The grouping is im-portant because it recognizes that two

fer to route most boards by hand andthen check my work using theautorouter.Checkingcanbe thereallyhard part to do by hand! When theprocess is complete, there will be aschematic diagram that exactlymatches the printed circuit board andvice versa.

Having an accurate and verifiedschematic is an extremely valuabletool for someone trying to modify or

debug a circuit-ven if that someoneis the original designer!OrCAD SDT can create a number

of reports related to the design. Theyinclude a parts list, designation list(Ul is an 8031), and so on, that helpensure compatibility between theprinted circuit and the schematic.

A typ ica l d raw ing ma de w ith OrCAD m ight inc lude ind iv idua l ga tes, co mp lete ch ips, and bused signa ls. This sam ple w as O U t p U t On 7

p lo t te r w ith a line - t ipp ed pe n .

Oc tober /Novem be r 199 1 61



SETTING UP

OrCAD has chosen to use an in-stall program for setup and to trans-mit updates. There is a total of fourl.ZM-byte floppy disks on which thesoftware has been archived (com-pacted). One of the disks marked “IN-STALL” is placed in A: drive and theuser types the word INSTALL fromthe prompt. The install program asksquestions about hardware and libraryrequirements to customize the sys-tem. Nothing could be easier. The pro-grams are installed in a well-orga-nized way in several subdirectoriesandchangesaremadeto~~~~~~. SYSand AUTOEXEC . BAT automatically.

The programs come with fivemanuals including: Installation andTechnical Support Guide,OrCADSDTUser’s Guide, OrCAD ESP Environ-ment User’s Guide, Text Editor User’sGuide, and OrCAD SDT Reference.

The manuals alone are not par-ticularly helpful if it is the first timeusingschematiccapturesoftwaresincesome of the lingo can be confusing. It

isdifficulttodistinguishbetweenwhatmight have been problems with thedocumentation and my limited un-derstanding of the design process andimpatience when I started usingOrCAD. I needed the software rightaway, so I began by drawing somesimple designs and working things

out with the Reference Manual inhand. I don’t recommend reading allthemanualsbeforestarting. Itisbetterto jump right in and then go back laterto learn some of the finer points.

A sample schematic is includedwith the program and is discussed inthe user’s guide. Following the tuto-rial with the manual in hand is veryhelpful, but cannot cover all of thetopics encountered when designing areal schematic for a project.

ORCAD’S LATEST EFFORT

My one major complaint aboutOrCAD SDT when we first purchasedit was that each program of the collec-tion had to be invoked from the DOScommand line with whatever switches

and file names were appropriate. Forexample:

NETLIST MYBOARD SCH

C:DESIGN\MYBOARD.NET /S

is the command to create a net listfrom a drawing called MYBOARD. SCH

and place the fileMYBOARD. NET)

insubdirectory c : \DESIGN. The satthe end signifies that the file should bewritten in the format for the TangoPCB program that I use for layout. Itrequired great feats of memorizationfor those who didn’t use it every day,or lots of looking through the manual.

OrCAD has recently improved thesoftware (Release IV) to include anintegrated windows-style environ-ment that they call ESP. On-screen‘buttons” are used to select programsand set up options. The programswitches are replaced by setting up alocal environment with the switchesset as defaults. The result is an intui-tive user interface that works well.

The new environment is not per-fect, though. The programs are not

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62 CfRCfJfl CELLAR INK







SPECIALSECTION Schematic CaptureKen Davidson

with SchemaI

So what’s wrong with notes on paper napkins? Sure, they can be a little

mushy to write on, and you can’t fit a whole lot onto one, but they travel real

well, and once you’re done with them, you can use them to wipe the sweat

from your brow.

Steve tells stories of the “good old days” when he could sketch out a circuit

on a dinner napkin, bring it down to Ray Long’s to have a board laid out (see

“Bringing in the Pros” in issue 20 of C IRCUIT CELLAR INK for more on Ray’s

company), and have a working board in hand in short order.

Those were also the days whenCircuit Cellar projects tended to beess complex. The PC boards were allaid out by hand using several layers

of acetate, rub-ons, tape, and a good,harp knife; circuit designs were san-ty checked by the designer’s keen eye

and perhaps an associate looking overhis shoulder; and the person layingout the PC board had to be able tomanually swap gates within a pack-age or catch a bad pin number on thechematic. Invariably, when the pro-otype PC board came back for firstest and didn’t work, at least half ofhe problems could be attributed toayout mistakes.

About six years ago, we startedooking for a better way. Reasonably

priced schematic capture packageshat might be considered for serious

professional use were just starting tohow upon themarket. Wealso started

working on Ray to upgrade his shop,rying to convince him that his pro-

ductivity could jump markedly if hewere tocomputerize. Up to that point,here wasn’t a piece of silicon to beound in his shop.

ClRCUlJ CELLAR INK

Omation Inc. was trying a novelidea for the software industry: a freedemo disk containing a version of thesoftware that was fully functional ex-cept for some key features such assaving or printing. We gave them acall, received the disk, and have beenusing Schema for all our schematicsever since.

SCHEMATIC CAPTURE SOFlWARE

Before I get into Schema proper,let me go over a few schematiccapturebasics. There are two key questions toask when looking at any software:what will the software do for me thatI either can’t do now, can’t do effi-ciently, or can’t do effectively (i.e.,how will it save me time?); and is iteasy enough to use that I’ll continue touse it and not be hindered by it?

Foranyonenotfamiliarwithsche-matic capture packages, it is useful toconsider the idea that they are to cir-cuit design what word processors areto writing. A good word processordoes not make a good writer (as I’moften reminded), but a good writer

can often dramatically improve hisproductivity by using a good wordprocessor. He is able to shed many ofthe more mundane and error-pronetasks onto the computer and direct allhis energies to actually writing.

Most of the designer’s (writer’s)time will be spent entering new infor-mation and manipulating and modi-fying it. This stage is where a gooduser interface is a must. If the designerhas to labor at using the computer, it’snot going to save him any time andhe’ll be less likely to use it in the fu-ture. All schematic capture packagesI’veseenuseagraphicalinterfacewithat least one on-screen menu and support (if not require) the use of a mouse.They allow the designer to manipu-lateeverythingassociated withacom-ponent as a single unit. For example,the outline of the part, the pin num-bers, and the pin descriptions are allintegrated. Individual components orgroups of components may be movedanywhere on the screen and wire con-nections may be changed at any time.

Humans are the only ones whocan lookat a design to determine if it’s



SCHEMATIC CAPTURESOFWARE EECAD)

going to work, but the computer canoften helpcatch theobviousmistakes.A good piece of schematic capturesoftware will do a “design rule check,”which is akin to the spelling checkerfound in most word processors. (Theword processor won’t tell you whetherthe critics will like your piece, but it

can at least make sure you’re usingwords from the English language.)The design rule check looks for suchblundersasmultipledriversconnectedtogether, inputs left floating, multiplecomponents with the same referencedesignator, and labels used in onlyone place.

PC board layout software to ensureaccurate transfer of the design fromthe symbolic schematic stage to thephysical hardware stage. Similarly,word processors often support nu-merous file formats to ease the transi-tion from, for example, the author’sIBM PC to the publisher’s Macintosh.

Schema includes full mouse support. While not required, you’d haveto be a fool not to use one.

SCHEMA: THE SCREEN

Once your design is complete, youmay elect to print or plot the finishedproduct. Most schematic packagessupport at least HPGL pen plotters

and dot matrix printers. Most alsosupport a broader range of plottersplus laser printers. Likewise, mostword processors have a list of sup-ported printers longer than their listof supported features.

The majority of the screen is con-sumed by the main drawing area.Downtheleft sideisamenu, thetopofwhich always contains the top-levelcommands while the bottom changes

depending on what command hasbeen selected. At thebottomleftof thedrawing area is an optional screencoordinate box that is continuouslyupdated with the current location ofthe cursor. Many different displayadapters are supported, including allthe major super VGA boards. It was apleasure to upgrade from a vanillaCGA to an 800 x 600 VGA display.One of the 1024 x 768 boards on themarket would provide an even larger

window onto the schematic beingdrawn.

PART DEFINITIONS

In order to aid in the transfer ofyour finished design to the next stage,most schematic capture packages alsosupport the generation of a “net list’(which is usually the reason for usingthe software in the first place). Any

connectionbetweentwoormorecom-ponents is called a “net.” A net list isnothing more than a list of compo-nents on the board and a list of con-

When we received the demo diskand tried out the package, the moststriking feature at first glance was itsuser interface. Most drawing pack-ages allow you to see only a staticview of your drawing and force you touse scroll bars or awkward keyboardcommands to move to other parts ofthe schematic. With Schema, when

thecursorreachesanedgeofthedraw-ing area, the whole area starts tosmoothly and quickly scroll across theschematic, stopping either when thecursor is moved away from the edgeortheedgeoftheschematicisreached.With such a feature, the designer canvery easily move from one part of theschematic to another without lifting afinger or moving the cursor very farfrom the area of interest. It also elimi-nates the frustratingly slow screen

redrawsoftenencounteredwithdraw-ing packages. If you want to get abetter feel for what the drawing lookslike as a whole, a number of zoom

The first step in drawing any sche-matic is defining the components.Omation includes extensive librariescontaining all the popular logic fami-lies (LS, CMOS, etc.), microprocessors,memory, and, of course, active andpassive analog components, so

chances are most of the parts you’llwant are already defined. For thosethat aren’t, or if you’re not happy withthe predefined version, you can go to

nections between them. It is used by levels are supported. the object editor.

AO-A15 u3

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ENABLE1 74115138

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200CElREAD 2200E

Com par ing the sam e c i rcu i t be twe en Sche ma and OrCAD show s that both prog ram s ge t the job d one , but eac h has its own SW/e.

Sc hem a’s output w as do ne o n a n HP LaserJet p r in ter.

Oc tobe r /Novembe r W 65



SCHEMATIC CAPTURE SOFtWARE EECAD)

Theobjecteditorisintegratedintothemaindrawingprogramand hasanalmost identical user interface to theschematic editor. It includes the es-sentials for drawing boxes, circles,bitmapped images, labels, pin num-bers, and so on. You may also editanything already on the screen.

In order for Schema to be able todo a design rule check, it must knowmore about the component than sim-ply what its schematic symbol looks

For anyone not

fam iliar w ifh

sc hem at ic c a pture

p a c ka g es, it is

use ful to c onside r the

id ea that they a re fo

c irc u it de sig n wha t

wo rd p roc esso rs a re

fo w riting .

like. For each pin on the component,

you must tell Schema what its numberis and whether the pin is input, out-put, bidirectional, tristated, analog, or“don’t care.” Schema uses the pin func-tion information during postpro-cessing to make sure all the parts areconnected in harmony, and uses thepin number information to generatethe net list.

A somewhat confusing aspect ofSchema (but powerful at the sametime) is the differentiation between

‘body objects” and “named objects.”When we first started using the pack-age, the distinction between the twowas vague, but the documentation hasbeen improved over the years. A bodyobject is the graphical symbol usedwhen the component is put on theschematic.Bodyobjectsmaybenested(and are often called “nested objects”);for example, a simple inverter objectmay be defined once, then used mul-tiple times when defining body ob-

jects representing a 7404, 7406, and7414. All use the same basic shape, but

may have slightly different labels oradditional symbols.

When a component contains sev-eral gates within the same package, aeach gate must be defined separately.In the above example, you must de-fine each of the six inverters in the7404 package as separate body ob-

jects. Granted, you can define a singlegate, then make copies and smallchanges to do the rest, but it can still betime consuming.

An even bigger nuisance is hav-ing to define each style and rotation ofa gate separately. To again use our7404 example, if we want one invertersymbol with the inverter bubble onthe output side and one with thebubble on the input side, plus all fourrotations of both styles, we must de-

fine 48 separate objects to cover all thebases. Luckily, Omation has alreadydone the work for virtually all thepopular gates in use, so you may neverrun into it.

A named object is used to tie to-gether all the body objects associatedwith a particular component and isused when placing a component onthe page. It is a textual description ofthe component that includes yourstock number, a short description of

the part, and the name of the bodyobject family. To use the 7404 exampleonce more, the six main body objectsmaking up the package might be calledTM-lA, TO4-lB, on up to TO4-lF, soyou include the “T04” family in thedescription of the “7404” part. Thehierarchy helps a great deal when de-fining a component with several sec-tions, but can be a hassle when defin-ing something like a microprocessorthat consists of just one body object.

THE SCHEMATIC

Defining the parts is the boringpart of the process. Once done, youcan start the actual drawing of theschematic. The schematic editor al-lows you to place any predefined parton the page, assigning a referencedes-ignator and, when necessary, a valueto the part. The part requested may bechanged at any time, so if you find that

you want a different value resistor ora different gate in the same package,

you can make the change without hav-ing to delete and re-place the part.

Any pin on a part that has beenproperly defined has a perpendicularline at one end denoting where thewires are to be attached to the part.Wires also have arrows at each end, somaking sure the arrows always touch

the perpendicular on the parts’ pins isthe best way to be sure connectionsare made properly. Wire arrows andpin perpendiculars may be turned offat any point and are never printed inthe final schematic.

Anotheraid in getting thingslinedup is a redefinable grid and optionalsnap to the grid. Leaving the grid andsnap on all the time is another goodway of assuring that proper connec-tions are made.

When connections must be madebetweenpartsthatareatoppositeendsof the page or on different pages alto-gether, a wire may terminate at a la-bel. This label becomes the name ofthenet,andanyotherwiresconnectedto the same label elsewhere on thedrawing are also connected to the samenet. To clarify the drawing, groups oflabeled connections may be bused to-gether. The schematic editor providesfat and narrow arcs and lines for the

creation of buses. The arcs and linesare only cosmetic, however, since it’sthe labels that determine to which netsthe wires are connected.

I find that overuse of buses andlabels make the final drawing confus-ing and difficult to read. I like to makedirect connections whenever possible,using buses only for data and addresslines. If control and other signals mustgo from page to page, I always try tobring the individual signals to either

the left or the right side of the page.That way, a quick glance down thetwo sides of the page will tell you if aparticular signal is used on that page.When all the interpage signals arebrought to buses at random points onthe page, you’re forced to scan theentire contents of every page to findthe signal you’re looking for.

Rearranging portions of the sche-maticiseasy.Simplydragaboxaroundthe area you want to move, grab the

corner, and the whole area moves inunison. When released, any wires that

66 CIRCWJ CELLAR INK



crossed into or out of the moved areaare still connected, though often endup as diagonal lines that must later besquared off and cleaned up. The ad-vantage of this “rubberbanding” ef-fect is that once you make a connec-tion with a wire, that connection isnever broken until you delete the wire.

It’s just one more way that the com-puter can be used to keep track of thelittle details while you concentrate ondoing the design.

As I mentioned when describingthe object editor, support for rotatedparts is pretty slim. Recent versions ofSchema include a rotate command inthe draw and edit menu entries, butthe command relies on the existenceof rotated versions of the part in one ofthe libraries. If a rotated version hasn’t

been defined, one must be definedbefore a rotation can take place.

Scaling isn’t supported atall. Oncean object has been defined, its sizecan’t be changed unless you go intothe object editor and redefine it. Un-less you’re trying to fit a D-size draw-ing onto a B-size page, I don’t thinkyou’ll miss scaling.

POSTPROCESSING AND PRINTING

Once the drawing in complete,there is a host of postprocessing thatmaybedone toit. While theobjectandschematic editors described above areintegrated into one program, the restof the Schema package consists of sepa-rateprogramsforeachpostprocessingtask.

As I mentioned before, a designrule check may be done to look forsilly drawing mistakes. A list of parts,sections within each part, and refer-

ence designators may be produced, aswell as a complete bill of materialswith your own stock numbers next toeach component. The net list may alsobe generated at this point.

Almost all PC board layout pro-grams use their own net list format.Omation includes a very useful utilitythat converts their net list format tothose used by the major PC boardlayout programs and systems. Ourlayout house (Custom Photo) pur-

chased a Calay system in response toour prodding, so the final step we

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Oc t o b e r / No v e m b e r 199 6 7





DEPARTMENTS

Firmware Furnace

I I

From the Bench

Silicon Update

Practical Algorithms

wpuge 103

ConnecTime

e-)Starting C

OK , even I admit it now:C for microcontrollers has arrived.Whether you like it or not, if you don’tspeakCyouwon’tbeahitattheparty.Indeed, a recent RFQ arrived stating“the software will be written in the C

programming language” withoutspecifying the CPU. The handwritingis on the wall!

Rest assured that Firmware Fur-nace won’t turn into Yet Another CColumn. There are cases where as-sembly language code is still required(and I will gleefully point them out),but, for the most part, source codelistings will be in C rather than assem-bler. For us, C will serve as a “high-level assembler” rather than a “low-

level” language.During the past two years I used

Avocet C for many of my projects,some of which you have seen here.

Judging from the BBS traffic, though,the market leaders are Franklin andArchimedes. Any of these three willset you back about two kilobucks,whichisalotofcointodropin theslot,especially if you are not convinced Cis a Good Thing.

Unfortunately, switchingbetween

C compilers is not as simple as com-peting vendors would have you be-lieve, quite apart from the up-frontcost. Each compiler accepts a differentsubset of the C language, the run-timelibraries are nearly disjoint, and theassembly language interfaces are ut-terly bizarre. While “straight C code”will port, your programs won’t be-cause they will depend on featuresunique to your current compiler andassembler.

The good news is that the markethasroomformore than just thebiggies.

A cursory glance through any maga-zine catering to the firmware tradewill reveal several C compilers pricedwell under the tropopause. For thiscolumn I will use the 2500AD com-piler, which I bought earlier this year

for a specific project that didn’t suitAvocet C. It costs $600 and includesthe compiler, assembler, and an as-sembly language simulator.

While I don’t intend to start areview series, either, I will also look atthe Micro-C shareware compiler fromDave Dunfield in the next column. Ifyou thought you couldn’t afford C,the times they are a-changin’ (and forthe better, too).

IN THE BEGINNING

The C language makes severalassumptions that just aren’t true afterthe CPU emerges from a hardwarereset. For example, althoughuninitialized C variablesare supposedto be set to zero, 8051 hardware doesnot clear either internal or externalRAM before executing the instructionat address OOOOh. And the hardwarehas no idea of how to load the proper

values into C’s initialized variables,either.Obviously, all variables must be

set up before the first line of C codeexecutes, so the code that gets controlimmediately after a hardware resetcannotbe writteninc. Nomatterhowsimple the C code, some assembly isstill required!

Every C compiler package in-cludes a startup routine that must belinked with each C program to handle

these initializations. Avocet calls itCRT5lx, 2500AD refers to C8051xR,

70 C IRCUIT CELLAR INK



FIRMWAREFURNACE

Ed Nisley

x” marks the spot for the memorymodel identifier, which I will discusslater, so you must use the appropriateroutine for your situation.

Each company decides what func-tions should occur in the startup rou-tine. Avocet includes just memory andstack initialization, 2500AD heaves inring-buffered and interrupt-drivenserial handlers, and Micro-C just setsthe hardware stack pointer. You mustreview the contents of the file to makesure that you arenot getting too much,

too little, or the wrong kind of initial- the *RD and *WI3 signals. I/O portsization for your purposes. Contrary to are memory-mapped in the Externalpopular opinion,changing the startup data space, so there is no separate I/Ocode is not sinful-it can be essential! addressspaceasthereison8086CI’Us.

MEMORY MODELS

The 8051 architecture defines sev-eral different address spaces. Programinstructions are burned into EPROM,which is located in Code space andaccessed by the *PSEN logic signal.Variables can be in either Internal orExternal RAM, the latter accessed by

Internal RAM has only 128 bytes(in the 8052 derivatives, 256 bytes) tohold the CPU’s working registers, thehardware stack, and 128 directly ad-dressable bit variables. The workingregisters are not usually accessiblefrom the C code level. The hardwarestack may or may not hold C functionparameters, but will always hold thefunction return addresses. Bit address-

1+ c310 uF

N o t e o r d e r !

Figure l--The c ontro l ler for the sam p le LED d isp lay is a t yp ica l 8032-based c irc ui t reg ula r rea de rs shou ld b e v ery fami l iar w i f h .

October/November 199 I 71



ing varies by compiler; some havegood support, others none at all, whilesome have rather clumsy support thatisn’t worth using,

A further complexity arises whenexternal hardware combines theCodeand External RAM address spaces byORing the *PSEN and *RD signals.The Code space must start at addressOOOOh because that’s where the CPUbegins execution, so RAM must startat a higher address (typically 2000h or8OOOhl to avoid collisions.

Most 8051 C compilers support atleast two memory models, known asSmall and Large. The Small modeluses only Internal RAM, while Largeuses External RAM for variables andthe C parameter stack. Of course, thememory model names are not stan-

dardized and there are several per-mutationsandcombinationsavailable.For example, Micro-C’s Mediummodel corresponds to Avocet’s Large,while 2500AD uses the terms Internaland External Mode. Read the manualcarefully!

TWINKLE, TWINKLE, LED

There’s nothing like a good hard-ware project to justify some softwareexperimentation and find how thingsreally work. I’ll use the 8032 systemshown in Figure 1, which will runwith the Small memory model be-cause it has no external RAM. Figure 2shows the “output device,” a rectan-gular array of 40 multiplexed LEDs.

Each of the 40 LEDs is associatedwith a C variable located in the 8032’sInternal RAM. The firmware countsthe variable down at a regular rate.When the value hits zero the firmwareupdates the LED, turning it OFF orON as needed. The result is a pleasantblinking array that’s sure to brightenup any office decor. When you see it in

action you may be reminded of thestatus panels in those old Star Treksets...the ones before the fake large-screen CRT displays.

A jumper changes the displaymode so the LEDs blink briefly whenthe corresponding timer hits zero. This

mode ismore frenetic, suited for thoseoccasional high-caffeine days.

Listinglshows BLINKBOX S~~~~loop. There are two key data struc-tures: the Timers array holds the 40variables that determine when eachLEDchangesstateandthe~nodeDataarray, which holds the 40 bits (fivebytes)thatmapeachLED.TheDataIDand B it Ma s k variables convertTimerID into an AnodeData indexand bit location.

Although you might thinkAnodeData should be located in thebit-addressable section of InternalRAM, it turns out that the 8051 in-struction set doesn’t have a general-ized “set bit” instruction (despite whatyou might conclude from the 8051App Notes). The bit location is en-

coded in the instruction, rather thanbeing held in a register, so 120 differ-ent instructions are necessary to turn40differentLEDsonandofforcomplement their state. It is far simpler togenerate a byte index and mask insoftware and do the bit twiddling “by

8 x 3.3K

0 x 2N2907F\

8 x 3 9

5 x 4 . 7 K

FigWe 2--The f lashy pa rt of the sample c irc uit is the a rra y o f 40 1EDs ar rang ed in iv e row s and eight c olumns.

7 2 ClRCUIT C ELLAR NK















RedefiningRemote ControlNow You See ‘em--Beep-Now You Don’t

FROMTHE

BENCHJeff Bac hioc hi

Thank you American Airlines. It is

great to be back in the USA. Don’t get

me wrong, it’s not that I didn’t like

Mexico. It’s just a bit difficult withoutknowing adequate Spanish. 5,” “no,”

and “gracias” won’t cut it when you

need to hold an intelligent conversa-

tion Like, “What do you mean I don’t

have the proper papers to pass cus-

toms? That’s my plane!” Believe me,

you don’t argue with a uniformed

guard brandishing a “pistola.” I felt like

a malformed part on an assembly line:

Honk! The quality control inspector

checks my specs and presses the re-

ject button. Into the pile of discarded

parts I fall, along with the other bodies

who can’t speak Spanish. I’ll never say

another bad word about airlinecounter personnel, the last refuge for

a “gringo.”

Mexico is a strange combination of high and lowtechnology. Road repair is done with pickaxes, shovels,and wheelbarrows; no heavy equipment. Businessmen,however, wouldn’t be caught dead without their hand-held cellular phones. It became obvious by the number of“boops” and ‘beeps” heard during lunch (from 2 PM to 5

PM) that this was when most deals were formulated. Dealslike this one; the one which brought me to Mexico.

I IHANDS ACROSS THE BORDER

Beinghiredasaconsultant isalot likeplayingfireman.One has to know which type of extinguisher will put outthe blaze in the shortest period of time, with the leastamount of damage. If the fire has not grown too large, you

can salvage enough to create success out of failure. Thetask at hand was not a three-alarm fire, but red tapepromised to stoke the blaze.

The biggest failure of this project was a lack of firmspecifications. The product had to be continually modi-fied, because the rules changed depending on where theequipment wasbeingused. Hand-wired prototypes wouldnot work consistently in the field. This meant deliveryschedules were now approaching impossible.

I want to see specifications before I start any project.Without rules, no one can play the game fairly. Designingdata acquisition or any other type of equipment is impos-

sible without complete requirements, I’m not suggestingthis product had been designed without any specifica-tions. I’m indicating that these were ideal specificationsand only realistic in an ideal environment. The actualenvironment can play havoc with what you might expectto see. Environmental noise, from subaudio through RF,can have an impact on your data. In most cases, simply bylooking at the data in the actual environment, you candetermine if the environment is adding anything to theraw signal. If it is, you can make appropriate changes in thespecifications to eliminate it. It is important that you andyour customer agree to the specifications prior to any

agreement or, like this company, you may never get out ofthe design stage.

LET’S SIMPLIFY THINGS

Simplifying a client’s design can often result in majorcost saving, especially when production quantities arehigh, and establishes the true value of hiring a consultant.For instance, this client’s product used a aptop as a serialI/O device permanently attached to the product. Otherhardware could be used here to simplify the product andmake it more user friendly.

One of the most exciting products I’ve seen lately is theconfigurable legend switch (see “Silicon Update” in Issue

October/November J 99 J 79



PI+-. I

P16-

PlSdPM+p13-P,Z$PI,--

Pd-FOR LM2136

A NN UN CI A TO R

40KHz OSCILLATOR I 01DUIIVPi) L

Figure 1 -The complete schematic for the ha nd-held LCD terminal doe sn ‘ t inc lude muc h mo re tha n an 875 controllerplus som e sim p le interface circuits.

#20,April/May199l,ofC1~currC~~~~~INKforrnoreinfo).These are expensive little buggers, but increase flexibilityto the point of payback in many cases. This idea could beused to reduce the number of keys necessary on a product,like the one being developed in Mexico.

Every time I pick up my calculator, my mind goes intoa whirl. Every key has a legend printed on it, as well as oneabove it and one below it. Some of them are printed inwhite, while others are printed in orange, green, orblue. Ithas a shift key, a mode key, and arrow keys. It doesn’t havea help key. You might have such a calculator somewherecollecting dust because you’ve lost the manual. Unless I

used it every day, I would quickly forget the correct keysequences to do various functions. Powerful, but not userfriendly.

A better approach for I/O would be to use a simpleLCD display to provide output and redefine the functionsof a few keys. You can see this being introduced on somenewer test equipment.

HASTA LA VISTA

During the five-hour flight back to Connecticut (thanksagain, American), my mind slipped back to thoughts of

home control. I couldn’t think of a much simpler approachfor I/O on my home control system.

80 ClRCUlT C ELLAR NK

I began scratching out bits of circuitry on the back ofmy drink napkin. My initial thought was to use an RTC52with an RTC-LCD board, which has a LCD display drivenby memory mapped I/O. I realized immediately that itwould be overkill. A micro which receives ASCII serialinput and directly drives an LCD panel could scan keysand send serial ASCII with few, if any, additional chips. An8751 would serve well here. That would eliminate anaddress latch, RAM, and EPROM. With a few glue chips Icould map the LCD into I/O space. No, that’s not what Edwould do. I remembered his “Firmware Furnace” col-umns on LCDsand keyboards (see issues and 16). I felt

a bit of a challenge here-I’m not much of a software junkie. “Just to keep the glue to a minimum,” I kept sayingover and over, trying to convince myself that it was neces-sary.

PALM-SIZED TERMINAL

I’ve previously written routines for 4 x 20 and 8 x 40

LCD displays. Since the LCD will be mainly displayingmenus for my home control system, and key definitionswill take at least one line, the small display won’t beadequate. This design will use the larger display which has

a physical size of 2.5” x 8” . See Figure 1 for the completeschematic of the terminal. Only the read and write subrou-





been pressed. The port has internal pull-ups and each of the port’s eight bits areconnected to one of the push-buttonswitches. The other side of each switch isgrounded. The port will read an FF hex ifno switch is pressed or a low on theparticular input bit connected to thepressed (grounded) key. The routine

could be rewritten for multiple key en-tries or even a 4 x 4 keypad.

Let’s take a look at a few possibilitiesusing the display and eight keys. Figure 2shows a simple one-key entry. From this“sub-sub-sub” menu (Living Room/X-10 Control/Lighting), the choices are exitback to the main menu, previous menu(X-10 Control), select a lighting device tocontrol (see more items), or redisplay thisscreen (it may have been garbled in trans-mission).

Photo 2-lhe 8 x40 dispk~y allow s the use of very descriptive menu selections and up to eight cho ices ac ross the b ottom of the display.

If digits O-9 are needed, it requires a two-key sequence As you can see, there is a good deal of flexibility in theas shown in Figure 3. If the column with 2,5,8, and 0 is amount of information and how it is presented. Of course,chosen, a second screen is displayed eliminating the if you think in binary, any of the ASCII characters can beunselected items. Rotating the selected column eases de- entered directly by pressing the appropriate keys usingfinitive selection as shown in Figure 4. This can be ex- seven of your ten fingers. For me and my ten thumbs, thispanded if necessary to include alphanumeric characters is out of the question (besides the fact that I am acknowl-and still only require a two-key sequence (see Figure 5). edging only single strokes).

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82 CIRCUIJ CELLAR INK

ReaderSewce+217



Living Room - X-10 Control - Lighting1 - Table Lamp2 - Reading Lamp3 - Floor Lamp4 - Ceiling Lamp

MAIN PREV SENDMENU MENU 1 2 3 4 MORE SCRN

Figure 2 Seve ra l/ eve /s ofmenus can be easi ly traversedusing the

pu sh buttons.

TALK BACK

If you use a PC, then you probably know when youhear a beep, it probably means something just went wrong.If you’re using a Macintosh, you might hear a “raspberry”

instead of a beep. In any case, this audible sound is enoughto get your attention. These indicators give a gentle re-minder (except, perhaps, in the case of the raspberry) thatyou should take a closer look at what you just asked themachine to do.

Similarly, there is a TSR I’ve seen that can generate aclicking noise whenever a key is pressed on the PC’skeyboard. This gives an audible feedback when typing,similar to the old IBM keyboards or an even older type-writer. Not a big deal, but can give a bad typist a bit moreconfidence. Such feedback is almost mandatory on flatkeypads, like the ones used on microwave ovens. You’ve

probably seen the technique used everywhere, from oc-tane selection at the gas station to your bank’s ATM.

Piezoelectric devices produce a loud sound output fortheir size and are therefore a good choice for annunciators.A port pin on the microprocessor serves well as a piezodriver and indicates debounced keystrokes from the eightpush buttons. It will also sound at the reception of a bellcharacter (07 hex), from the serial port. This way, thesource of the serial transmissions can get my attention orjust indicate the end of transmission.

Select the column holding your number

1 2 34 5 6

MAIN PREV 7 8 9 SENDMENU MENU 0 SCRN

1 igureJ-A tw o-step p roce ssisused wh en selec t ing from alarge l ist

of i tems. In the f irststep , the large group is div ide dd ow n to am u c hsm al ler group w ith the f irst b utton p ress.

RAM 4.5 x6.5" d

14 l/O lines and decoded DIP switch - Serial pWtw/ DB2$ti&%&3~k

BpSys in EPROM, w/ source code - RAM, l/O “&&rol f~& t’ ” F, d a *

Cross assembler included - CMOS and BASK: options a&@ &*,

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SILICON

1 ;mraFyE Nuts About RISC

G o on a Low -Fa t Ac o rn D ie t

A lmost three years ago, in the first issue of CIRCUIT CELLAR INK, I wrote short

piece entitled “RISC vs, Reality” in which I, with tongue somewhat in cheek,

attacked the RISC hype and zealotry then at its most strident.

The main point, admittedly presented with inflammatory rhetoric, was that

RISC was more a marketing ploy than a technological “revolution. m Essentially,

the RISC concept (which I was careful to point out, has some technical merit)

had devolved to mean any new chip which isn’t an 80x86 or 68xxx.

Since then, having failed to displace low-end PCs (i.e., 80x86- and 68xxx-

based systems), many RISC suppliers are pushing (hoping) for an “embedded

RISC” market to emerge.

For some reason, whenever I hear the term embeddedRISC I can’t help but visualize a “UNIX toaster.” Built-inmultitasking means you can burn more slices at once whilethe ubiquitous Ethernet port handily connects to yourcoffee maker. Even the fussiest chef won’t tax a 4gigabytevirtual address space.

Frankly, so far most of the embedded RISC offeringsare about as practical as a UNIX toaster. However, there ishope on the horizon as suppliers migrate their existing“CRISCs” (Complex RISCs, or UNIX chips optimized forcranking floating-point loops) towards “Retro-RISCs,”

whichattempt to recapture the simplicity and innocence ofthe original concept; kind of the micro equivalent of theMazda Miata.

As suppliers continue to strip unneeded UNIX bag-gage and cut prices and chip count into the realm of real-world controller feasibility, I imagine I’ll have more to sayabout embedded RISC.

Meanwhile, we can start with one of the oldest RISCswhich, thanks to its age, turns out to be a good example ofa Retro-RISC. Whether the Acorn CPU (now rechristenedthe “ARM” for Advanced RISC Machines) itself takes offor not is hard to predict. Nevertheless, I think we can catch

a glimpse of tomorrow’s popular embedded micros intoday’s ARM.

86 C lRC UlT CELLAR INK

HIGH-FAT CHIPS

The problem with most RISCs is that there is nothingreduced about them. In the beginning, the RISC argumentwas that a simple CPU and a complex compiler couldachieve performance similar to the opposite (i.e., complexCPU, dumb compiler) setup. This is meritorious-better tospend more initially for a fancy compiler if the payback issmaller/cheaper CPUs in each and every unit sold.

Somewhere along the line, reflecting various players’marketing agendas, the RISC pitch mutated from one of

“good performance at lower price” to “highest perfor-mance at any price.” Thus, we end up with “reduced”chips like the i86OXP with 2.5 million transistors and a$500+ price tag! Unless you’re designing the mother of alltoasters, it’s not very relevant.

In the quest for performance, traditional RISC featuresare being jettisoned left and right to the degree that theterm RISC has become meaningless technically (if in doubt,revert to the marketing definition: RISC = NOT [80x86 OR68~~x1). Even the feature most identified with RISC-LOAD/STORE architecture (ALU works only on regis-ters, not memory operands)-may be under attack. In a

recent review of a new controller chip featuring LOAD/STORE, one pundit noted that “programmers won’t ap-









video, sound, virtual memory MMU, and so on-that arelikely not needed in an embedded design.

Yet, designing an ARM-based system without themisn’t easy. The basic problem is the ARM-2 bus interface:there isn’t one! Well, of course there are address, data, andcontrol lines (Figure 51, but they need significant condi-tioning to connect to conventional memory and I/O chips.

For example, the ARM-2 relies on address pipelining

and burst transfers to achieve no-wait-state performancewith slow DRAMS. If you don’t use their outside memorycontroller (MEMC) chip (with MMU, video support, etc.),a few PALS will be called for unless you can afford a bigperformance hit. Siniilarly, without their IOC glue chip,connecting byte-wide static ROM, RAM, and I/O chipsisn’t easy. Speaking of ROMs, you’ll need four of themunless you roll your own “x 8 boot ROM” circuit. Need await state? Whip out those old 6800 clock stretch circuits!

I haven’t even mentioned the follow-on chip, theARM-3, since it seems to have just gone farther down thedesktop path. While it does have a slightly easier bus

interface, the major additions are 4K bytes of cache and adedicated coprocessor interface. In my opinion, cache is ofdubious merit in embedded designs since it blows deter-minism (how long, exactly, a section of code will take toexecute). If the ARM-3 had a way to use the cache as RAM,or even a way to lock key stuff in the cache, I would be moreinterested. As for the dedicated coprocessor interface, thepackaging penalty seems high (I’d rather not deal with

(which is fortunate, since the catalog doesn’t show any forsale). The ARM-3 may be fine for tutoring UK techno-tots,but it’s not going in my next toaster design.

BACK TO REALITY

There is hope for the ARM. Recently, control of thearchitecture has been spun off to a new company, Ad-vanced RISC Machines Ltd., with investment from Acorn(the original designer), VLSI Technology Inc. (chip

POWW

CbdcInputs ::

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System

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Figure 5-The ARM -2 features the no rm a l ad d ress, da ta . andcontrol lines,but they need sign i f ica n t co nd i t ion ing to c onnec t to conven t i ona l memory and I/O chips.

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foundry), and Apple. The involvement of Apple has in-spired speculation; my guess is the ARM core might endup buried in support chips designed for tomorrow’s Mats.

Meanwhile, ARM Inc. also supplies the usual varietyof tools running on the usual platforms: C compiler, simu-lator, assembler, linker,even (shudder) a UNIX port. WhileI don’t have specific quality info, the fact that the tools havebeen around a long time is a positive sign.

Anyway, the key point is that the new company is notconstrained to serve only one customer (Acorn/BBC) ormarket (educational PCs). Now, they have the freedom todesign chips that truly serve the embedded control mar-ket. Manufacturing is expected to open up as well sinceARM Inc. intends to license a variety of suppliers to offerstandard and custom variants based on the CPU core.

It wouldn’t be hard to make a highly integrated ver-sion of an ARM microprocessor. This would involve add-ing the modern bus interface features (chip selects, waitstates, DRAM refresh and high-speed access modes, etc.1and typical I/O functions (some timers and a UART or

two) found on contemporary competitors. The chip couldbe further enhanced (“tarted up” as they might say in the

jolly old U.K.) with a fancy interrupt controller, low-poweroperation modes, and similar bells and whistles. A la “MyFair Lady,” the once homely ARM can be transformed.

Even better, why not take advantage of the CPU’s tinysize to pack on a lot of (EP)ROM and RAM-say 64KB and4KB respectively. Since the on-chip memory could be

accessed much faster than external memory, performancewould be high and scale linearly with clock rate. With allmemory on-board, bus interface headaches disappear andlow-cost, low pin-count packages are feasible.

Thanks to its excellent efficiency (performance pertransistor), the ARM architecture is arguably one of thebest candidates to serve as the core of tomorrow’s 32-bit“C’ingle Chips. +

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Tom Cantrell holdsa B.S. in economicsandan M.B.A.from UCLA. Heowns and operated Microfuture, Inc. and has been in Silicon Valley forten years working on chip, board, and system design and marketing.

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I

PRACTICALALGORITHMS Measuring SubjectiveCharles P. Boe g li

Sound Levels

uccasionally the merit of an experimental paperstands uncontested for many years. Among such works isthat of Fletcher and Munson [l], defining the sensitivity of

the human ear to tones of various frequencies. Their curves(Figure 1) were the foundation of all sound evaluationwork for more than a half century. They show that the

sensitivity of the ear is reasonably linear with intensityabove about 1000 Hz. Below that, however, the response isnonlinear with intensity, dropping off more rapidly atlower levels than at midfrequencies.

This effect is familiar to audiophiles. When the level ofmusic reproduction is below that of a live concert, the“bass” control is advanced to restore satisfactory balance.The “treble” control, however, needs little or no adjust-ment for variations in playback level.

Instruments were soon developed for measuring soundand noise levels. The usual method for determining thesubjective noise level at any location was to pass the signal

from a calibrated microphone through a weighting filter toconvert the flat response of the microphone to the charac-teristics of the “av-erage” human ear[21. The subjective h

sound level was 1 2 0

displayed on ameter. 100

For weightingthecontributionsofvarious frequen-cies, the original

recommendationwas to use a curvecorresponding tothe inverse of thesensitivity of thehuman ear to a levelof 40 decibels abovea reference of lo-l6watt/cm2 [3]. Thiswas the “A”weighting filter.The “phon,” a unit

of loudness leveldefined as the

“loudness of a sound numerically equal to the intensitylevel in decibels of a lOCO-Hz pure tone which is judged bylisteners to be equally loud” [4], was the unit in whichloudness levels were expressed.

Obviously no linear filter can reproduce the ampli-tude sensitivity of the human ear. The proposed B-weight-

ing filter (which used the 70-dB equal loudness contourinstead of the 40-dB) recognized this fact. The originalsuggestion was to use the A-weighting filter if only a singlefilter were available. In more sophisticated instruments,the A-weighting filter was recommended for measure-ments up to 55 dB, the B-filter for measurements from 55to 85 dB, and a flat response for measurements of very loudsounds (85 to 140 dB).

Since the epochal work of Fletcher and Munson, otherworkers have modified and reinterpreted the curves. TheISO, for instance, wrote a standard 151 that presents curvessomewhat different from those of Fletcher and Munson.

The difference lies principally in the region below 1000 Hz,where IS0 curves are much more linear with level than theFletcher-Munsoncurves.

Examinationof the work insound and noiseevaluationthatfol-lowed on the heelsof Fletcher andMunson reveals acontinuing ten-

dency toward lin-ear treatment of theear’s response,long after the needfor it has passed.

I Thisarticle lays the basis for a com- pu ter algo ri thmthat evaluatessound levels withthe nonlinear Fletcher-Munsonr e l a t i o n s h i p srather than fixedFigure 1 -The or ig inal Fletc her-Mun son c urves we re d eve lop ed in the e a rly 1930s.





















rom: RICHARD KIMBALL To: STEVE CIARCIAabout 150 feet of cable. Any feedback on this would be appreci-ated.

How about current consumption, Steve? I’m trying to put some-hing together to function in the bush over a several-month Msg :25975eriod. I’d considered the 8031/52 route, but the specter of From: KEN DAVIDSON To: PHIL ROBERTSattery depletion prevented any serious evaluation.

The R5422 spec states that you should be able to go up to 4000

feet using 24-gauge wire at data rates under 100 kbps. Your 150

rom: STEVE CIARCIA To: RICHARD KIMBALL feet shouldn’t present any problems (that’s the reason why we’ve been supporting RS-422/485 on all our new processor boards).

Remember, the 8OC52-BASIC chip is CMOS. If you remove the5176 (RS485 driver) chip, the RTC typically pulls about 15-20

. If you reduce the need for RS-232 communication and canemove the MAX232, it drops to about 8-10 mA. Then, if youeduce the crystal frequency, it starts dropping dramatically. Ictually got one board down to 2 mA while still running a BASICrogram.

rom: RICHARD KIMBALL To: STEVE CIARCIA

Hey, that ain’t so bad! I’m counting my pennies and thinkingbout how I can short change my six-year-old this Christmas.hanks again.

The Circuit Cellar BBS runs on a IO-MHz MicromintOEM-286 IBM PC/AT-compatible computer using themultiline version of The Bread Board System (TBBS2.1M) and currently has four modems connected. Weinvite you to call and exchange ideas with other CircuitCellar readers. It is available 24 hours a day and can bereached at (203) 871-l 988. Set your modem f or8 data bits,

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rom: PHIL ROBERTS To: ALL USERS

Can somebody advise on the spec for cable lengths using RS-485r RS-422. I have an application which involves mounting a piecef RF hardware as close to its antenna as possible. The unit isresently using a BCC52 to format its nonstandard output to RS32and feed a computer. I’m looking at needing to drive through

SOFTWARE and BBS AVAILABLE on DISK

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ToordereitherSoftwareonDiskorCircuitCellar BBSon Disk,sendcheckormoneyorder to:

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Recderset i e 170




STEVE’SOWNINK

1Steve Ciarcla

The Circuit (Storm) Cellar

1 here’s a funny thing about New Englanders and Hurri-

canes. For most of the year we sit around fearing that the next

hurricane will blow us off the face of the earth, yet at the same

time we are thoroughly disappointed when a hurricane happens

to choose someone else as the target of opportunity. After all,

why go through all the preparations and not have the satisfaction

of a good story to tell afterwards.

All New Englanders haveanindigenous yearning to survive

through a particularly devastating hurricane and then narrate,

with particular exaggeration, all the details to future generations

of friends and relatives. “Boy, you should have been around back

in 1954. We had Carol on August 31, Edna on September 11, and

then Hazel on October 15 It took six months to dry out, and was

the worst...”

Right now I’m sitting in the Circuit Cellar waiting for Hur-

ricane Bob to zero in on me. I’m using a UPSbacked computer so

I don‘t have to rewrite this whole thing after the crash. Even with

the rather regular power glitches starting to occur, I’ve still got

one TV on a local station and another on the cable Weather

Channel. According to the latest reports, Bob’s headed straight

for the Rhode Island/Connecticut border. Unfortunately, my

house is 40 miles from Rhode Island on a hill surrounded by

potentially brittle trees.

Actually, I’m probably more prepared than most people to

make it through natural disasters, but I equivocate over terminol-

ogy like “survivalist” in any descriptions. I’ve already checked

the propane-powered backup generator. It’s one of those big

two-cylinder jobs that’s supposed to do the whole house. Given

all the electrical goodies around here, however, I have to shed

Let’s see, I’ve pulled out some extra tarps: three 5’ x 7, two

9’x12’,a17’x29’,anda27’x39’.I’vechargedthreeextra12-V100-

AH batteries for the pump, eight 12-V 6.5AH batteries for the

radios and TVs, and made sure the Circuit Cellar automatic low-

voltage lighting system is ready. There are the rechargeable

flashlights (7), the regular flashlights (6) and a box of two dozen

D-cells, the car cigarette-lighter-type fluorescent lights (31, and

two 12-V portable power packs (just in case). After all, there’s a

hurricane coming.. .

Let’s see, the AM/FM radio and a shortwave unit are ready

but, wait, what about a TV? The two sets operating behind me are115-V units. I don’t want to have to start the generator to use

them. Better go do an inventory of battery-operated stuff.

I guess I must never throw anything out. I was amazed at

what was on the shelves of the Circuit Cellar. There were nine

battery-operated TV sets, ranging from 1”-6” B&W and color

conventional TVs to the latest 3” and 4” color LCD units. Unfor-

tunately, no one ever discussed hurricanes with the designers or

each wouldn’t have had such varied operating voltages and

unique connector configurations. The lowest-power LCD units

had the weirdest connectors and operated at voltages like 9.8 V

or 10 V. The largest conventional color TV had a readily available

connector and ran on 12 V but would have consumed a whole

battery between commercials.

Here was the first obstacle and the storm was only an hour

away. Warm up the soldering iron, quick. Do I settle on a 1” 6-V

Panasonic unit and get a magnifying glass; whip up a quick 12-

V LM317-based adjustable regulator with assorted universal

output connectors and polarity reversers; swipe one of the ma-

Documents

Circuit.cellar.023.Oct Nov.1991