EDSIM.docx

7/27/2019 EDSIM.docx

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User's Guide

Home

Preferthe

Original?

NewEdSim51

SH

Aboutthe

Simulator

User's

Guide

Installation

Instructions

Examples

ContactUs

TheFundament

alSimulation

s

Beginner's Guide

to the8051 -Online

Site

Map

User's Guide

The Microcontroller Panelo The Bitfield

o Data and Code Memory

The Assembly Code Panelo Source Pane Unlockero Load and Save

o Copy and Pasteo A Few Notes on the Assemblero Debuggingo Breakpoints

The Peripheralso The Logic Diagramo The LED Bank, DAC and the 7-segment Displayso The LCD Module

o The Switch Bank and the ADCo The Comparator and the DACo The Motor

o The UART

o The Keypad
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New Features!

Get the latest EdSim51 version

The Dynamic Interface

Now the user

can switch

the

peripheralsto other port

pins.

Getmore

information.

Unlock the External UART

Clicking

on the

button

marked Uat the top

left of theexternal

UART

places theUART in a

separate

frame, as

shownbelow.

This framehas muchlarger text

windows

for

transmittedand
http://www.edsim51.com/installationInstructions.html#simulatorInstallationInstructionshttp://www.edsim51.com/installationInstructions.html#simulatorInstallationInstructionshttp://www.edsim51.com/simInstructions.html#LDAndDIhttp://www.edsim51.com/simInstructions.html#LDAndDIhttp://www.edsim51.com/simInstructions.html#LDAndDIhttp://www.edsim51.com/simInstructions.html#LDAndDIhttp://www.edsim51.com/simInstructions.html#LDAndDIhttp://www.edsim51.com/simInstructions.html#LDAndDIhttp://www.edsim51.com/installationInstructions.html#simulatorInstallationInstructions


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receivedtext.

Simply

close thisframe to

lock theUART

back in the

main

window.


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SyntaxHighlightingNow, assembly code

written in EdSim51 isautomatically syntax

highlighted.

Instructions are


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coloured blue,

assembler directives(such as ORG,

USING, etc) are

coloured purple,aliases (for example,

the assembler replaces

TMOD with theaddress of TMOD) are

coloured orange and

comments arecoloured green.

Switching off syntax

highlighting: if youwish to turn off syntax

highlighting, simply

right-click anywhere

in the assembly codewindow and respond

to the prompt.

Change the System Clock Frequency

Originally, the simulator ran with a system clock frequency

of 12 MHz. Now the user can enter a value for the systemclock frequency in MHz.

UART Transmitting HEX Data

Up until now, the external UART only

transmitted text - whatever the user

typed in the Tx field was transmitted to

the 8051. Now, a list of 8-bit numbers(written in HEX) can be transmitted. To

do so, the user encloses the list in curlybraces, each number separated by a

comma, as shown in the image opposite.

When text is transmitted, it is terminated


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by 0DH. This is not the case with a list

of numbers. In the example shownopposite, the four numbers 56, 3a, 23

and e7 are transmitted, nothing more.

If the user wishes to send {56, 3a, 23, e7} as text rather than a list of 8-bit numbers, the text

is escaped using the \ character. Therefore, \{56, 3a, 23, e7} in the Tx field would result in{56, 3a, 23, e7} followed by 0DH being transmitted to the 8051.

LCD Module

A simulation of the popular Hitachi HD44780

LCD module has been implemented for the

EdSim51 Simulator. And now CGRAMhas also

been implemented. Find outmore.

Zoom

For high resolution monitors, click on the zoom button. The zoom button islocated below the red Exitbutton.

Keypad Modes

Now the user can select fromthree modes of operation:

Standard- any number

of keys can be closed at

the same time.

Pulse- once the mouse

button is released the

key reopens.

Radio- in radio mode

only one key at a timecan be closed.

Keypad And External 1
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Interrupt

Until now the keypad could

only be implemented using

busy-waiting. It can still be

implemented in that manner,but it can also be used together

with the 8051 external 1interrupt pin, P3.3.

Note:this pin, P3.3, is also

used by the display-select

decoder, therefore multiplexingof the 7-segment displays

cannot be implementedtogether with the keypad

interrupt. To multiplex the

displays and use the keypad atthe same time, the keypad must

be implemented using busywaiting.

More information on the

keypad modes and the

keypad interrupt

Intel HEX Reader/Writer

You can

now saveyour

source

code inIntel HEX

format.

Or you

can writeC code

for the

8051using one

of many

available
http://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypad


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8051 Ccompilers,

then

import theHEX code

into the

EdSim51Simulator.

Find out

more.

Simulator Window Update

As with many microcontroller simulators, EdSim51 allows the user to either step through a

program, executing a single instruction per step, or to run the program continuously. In theoriginal EdSim51 design, when running a program, the simulator would execute oneinstruction, update the screen, pause for a quarter second, then proceed with the next

instruction and so on. This allowed the programmer to observe changes in the hardware and

registers for each executed instruction. However, while this is very useful for debugging, itmeant the user would need to wait a long time for things to happen (examples: data transmitted

on the serial port to appear on the UART, an LED flashing at half second intervals, etc).

The best of both:now the user has the choice. Using theUpdate Freq.drop down menu (shown opposite) the

programmer can choose how often the screen should beupdated. The choices are: update the screen after everyinstruction execution (the default), after 100, 1000,

10,000 or 50,000 executed instructions.

Type in a value:the options available from the menumay not be appropriate. Therefore, the user can now enter

a number rather than select a value from the list. For the

entered number to take effect, the user must hit Enter onthe computer keyboard.

Find outmore.
http://www.edsim51.com/intelHex.htmlhttp://www.edsim51.com/intelHex.htmlhttp://www.edsim51.com/simInstructions.html#updateFreqhttp://www.edsim51.com/simInstructions.html#updateFreqhttp://www.edsim51.com/simInstructions.html#updateFreqhttp://www.edsim51.com/simInstructions.html#updateFreqhttp://www.edsim51.com/intelHex.html


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The Microcontroller Panel

A screenshot of the

microcontroller panel.This gives the user access

to all the 8051's registers

and data memory.

Boxes that are white can beedited directly. Those that

are grey cannot. For

example, the port latch bits

can be edited directly bythe user, but the port pins

are controlled by theexternal peripherals and

the port latches and cannot

be edited.

When

themouse

pointer

is left tohover

over one

of the

registerlabels,

the

register'saddress

appears,

as

shownopposite

for the

PCONregister.


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The Bitfield

In the above image, the individual bits for the accumulator are shown (ACC). The user can enter

any address or SFR name in the blue box (replacing ACC) and the bits for that given address willthen be displayed. Also, if you let the mouse pointer hover over one of the bits momentarily, the

bit's description is displayed, as shown below:

The bit field for the TMODSFRis shown. Notice bit 2 is the

counter/timerbit. Also

notice the background is grey.This is because the TMOD

register is not bit-addressable -

the user cannot alter these bits

directly.

The PSWis bit-addressable,therefore the background ofeach bit is white and the user

can change any of the bits

directly.

The bitfield can be used to see

the bit pattern of any address

in RAM (0 to 7FH) by typing

the address in the blue box. Ifthe location is bit-addressable,

the bit backgrounds are white

and the user can alter any ofthe eight bits.

As with SFRs, if the location

is not bit-addressable thebackgrounds are grey.

Data and Code MemoryBy default, data memory is displayed. Any address in RAM (00H to 7FH) can be altered byentering the address in the blue box (labelled addr) and then entering the desired value in the

box to the right (labelled value).


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Displaying Code Memory

Code memory can also be examined and edited, as shown in the image above. To switch between

data memory and code memory the user clicks on the button that is labelled Data Memorywhendata memory is displayed and Code Memorywhen code memory is displayed.

The first 127 bytes of code memory are displayed. To view another area of code memory, enter

the start address in the blue box. The 127 bytes from the start address onwards will then bedisplayed. Again, like data memory, the address specified in the blue addrbox can be altered by

entering a value in the valuebox. However, it should be noted that this will result in the machine

code and the assembly program being different.

In the image above, the assembly code that generated the machine code (as displayed in code

memory) can be seen on the right.

Update Freq.

The user can choose to either step through a program (executing a single instruction per step) or

run the program continuously. When running a program, the rate at which the screen updates isdetermined by the setting in the Update Freq.menu.


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Using the Update Freq.drop down menu the

user can choose how often the screen should

be updated. The choices are: update the

screen after every executed instruction, after

100, 1000, 10,000 or 50,000 executedinstructions.

Or, if none of these options is appropriate, the

user can type in a number, then hit Enter.

The update frequency may be changed while

a user's program is running.

The Assembly Code Panel

A simple

assemblyprogram

is shown

in the

assemblycode

panel to

the left.This

program

runs in acontinuou

s loop,

displaying

thenumbers 0

to 9 and

back to 0

on thefirst 7-

segment

display. Asnapshot


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of its

execution

is shownto the

right.

When the background of the assembly codetext area is white is it editable. The

programmer can write code directly here, or

can load a program from file using the Loadbutton (dealt with in the next section).

When the program is ready for testing, the

user can either click on the Assmbutton to

execute instructions one at a time, or on the

Runbutton to run the program continuously.Either way, the program will first be

assembled. If an error in the code isdiscovered, a message is displayed in the

message box above the assembly code (with

a red background) and the line with the error

is highlighted within the code in red.

If the code assembles without errors, Assm

is replaced by Step, the text area's

background changes to light grey. The codecannot be edited at this point.

If you want to go back to editing your code,

simply click on the Resetbutton.

Source code window a bit small? Read about

the source pane unlocker below.

Source Pane UnlockerThe simulator was designed so that everything is visible on the screen at the same time - theinternal registers, the source code, the peripherals, etc. However, this means the code pane is

quite small. But it can be expanded.Read more.

Load and Save
http://www.edsim51.com/sourcePaneUnlocker.htmlhttp://www.edsim51.com/sourcePaneUnlocker.htmlhttp://www.edsim51.com/sourcePaneUnlocker.htmlhttp://www.edsim51.com/sourcePaneUnlocker.html


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The user can write code directly into the text box when it is in edit mode, or an existing programcan be loaded from a file using the Loadbutton. Similarly, code in the text box can be saved tofile using the Savebutton.

There are two file types handled. The first is plain-text. Assembly programs are saved as regular

plain-text files (often called text-only) and usually with .aor .asmfile extension. By default,this is the format used when saving your source code in the EdSim51 Simulator.

The

other

file typeis Intel

HEX.

The user

can

select tosave a

file in

HEXformat

by

choosingIntel

HEX

Files

from theFiles

ofType:

menu inthe Save

dialog

box.Find out

more on

loading

andsaving

IntelHEXfiles.

To make the simulator more user-friendly, the last directory accessed (either through loading a

file or saving a file) will be remembered. Therefore, the next time the user opens a file dialogbox by clicking on either the Loador Savebuttons, the dialog box automatically opens in the

last directory visited.
http://www.edsim51.com/intelHex.htmlhttp://www.edsim51.com/intelHex.htmlhttp://www.edsim51.com/intelHex.htmlhttp://www.edsim51.com/intelHex.htmlhttp://www.edsim51.com/intelHex.html


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Copy and Paste

You can select code in the assembly text area and copy it to the system clipboard using the Copybutton, the same as you do in your word processing package. This can then be pasted elsewhere

in the assembly text area, using the Pastebutton (if the text area is editable - white background -

if it is not, click Reset). Or you can paste the selected text into some other application (such asyour word processor). Similarly, you can copy text from another application and paste it into the

assembly text area.

A Few Notes on the Assembler

The 2-pass assembler with the EdSim51 Simulator is not a full-blown assembler. It does not linkmultiple files and only some of the directives you might expect are implemented. However, I feel

it is adequate for the beginner. Below is a list of its features:

All of the 8051 instructions are implemented, except for MOVXinstructions, as the

simulator does not handle external memory.

JMP relequates to either SJMP relor AJMP rel. LJMP relmust be

programmed explicitly.

Similarly, CALLequates to ACALL. LCALLmust be programmed explicitly.

SETand EQUdirectives are implemented.

ORGis implemented.

USINGdirective (states which register bank is being used) is implemented.

ARnequates to the register address, as specified by USING(if the register bank is not

specified prior to ARn's use, register bank 0 is assumed).

SFR names and SFR bit names equate to the appropriate address. HIGHfollowed by an operand in brackets equates to the high byte of the operand.

LOWfollowed by an operand in brackets equates to the low byte of the operand.

Labels are followed by a semicolon.

The default for numerical values is decimal. Hex values can be entered by appending H

after the number, or placing 0xbefore it. If His used, the number cannot begin with a

letter (example: F5Hmust be written as 0F5H). Binary values are entered by appending

Bafter the number (as shown in the image below).

The assembler is not case-sensitive.

Debugging


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Regardless of whether thecode is running or being

stepped, once the code

assembles without errors,

the address of each

instruction is displayed tothe left.

When stepping through

the code, the instruction

that was just executed isshown in the grey box at

the top, together with the

instruction's address

(example shown:Executed 0x2A: MOV

90H, A).

The next instruction to beexecuted, its address is

highlighted. (002CH).

Breakpoints

A breakpoint can be set by double-clicking the instruction's address, as shown in the images

below.


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Setting a breakpoint:When stepping through

the code, move the

mouse over the address

of the instruction and

double-click.

When the breakpoint is

set the vertical bar (|)

immediately to the right

of the address is

replaced by a star (*), as

shown in the image on

the right.

Removing a

breakpoint: A

breakpoint is indicated

by a star (*). To remove

the breakpoint, move

the mouse over the

instruction's address and

double-click. The *is

replaced by |.

Alternatively, you canremove all breakpoints

with one click of:

When the program is running and a breakpoint is encountered execution halts just before that

instruction. In other words, the next instruction to be executed will be the breakpoint instruction.The programmer can then step through the code, or run the program, from that point.

The Peripherals

Note: The logic diagrams in this section were drawn for the default peripheral interface. You

may wish to alter this interface, which you can do by clicking on the DIbutton (see the imagebelow). You can also view the logic diagram for the new interface by clicking on the LDbutton


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(again, see the image below).

Also, there are instances in the following section where the sharing of port pins is pointed out.

For example, the motor and the UART share the same port pins. This of course may not be true

in your case, if, for example, you move the motor to other pins.

The Peripheral Panel


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The Dynamic Interface Panel - remap the peripherals |full size image
http://www.edsim51.com/8051simulator/images/screenShots/dynamicInterfaceLarge.pnghttp://www.edsim51.com/8051simulator/images/screenShots/dynamicInterfaceLarge.pnghttp://www.edsim51.com/8051simulator/images/screenShots/dynamicInterfaceLarge.pnghttp://www.edsim51.com/8051simulator/images/screenShots/dynamicInterfaceLarge.png


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An Instance of the Dynamic Logic Diagram

The Peripherals:

ADC

Comparator

Four 7-segment LED Displays

LCD Module

UART

Keypad

LED Bank

Bi-directional Motor

Switch Bank


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DAC (output displayed on oscilloscope)

These image on the left shows what is connected

to each of the 32 port pins. If a pin's descriptionis too long to fit, you can see the full description

by hovering the mouse over it, or by clicking onthe zoom button (see below).

Zoom

Click on one of the buttons marked + to displaythat port's connections in a separate window. Anexample for port 2 is shown below.

Port Pin Connections

The logic diagram below gives details of the peripheral interfacing.


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EdSim51 Simulator Peripheral Logic Diagram

The LED Bank, DAC and the 7-segment Displays

As can be seen in the diagram below, the LED bank, the DAC inputs and the 7-segment display


23/44

data lines all share port 1.

The selection of which of the four displays is enabled is done via P3.3 and P3.4. These port pinsare applied to a 2-to-4 line decoder, the outputs of which are applied to the base of transistors

that enable/disable the displays.

Logic diagram showing the LED bank, DAC and 7-segment display connections only.

The decoder is enabled via a logic 1 on P0.7. This pin is also applied to the DAC WR input,which is active-low. Therefore, to write data to the DAC the programmer disables the displays,

which also has the effect of enabling the DAC's data lines. Data can then be written to the DAC.Whatever is on the inputs when the WR line is taken low is stored in (or written to) the DAC's

internal register and remains there after the WR line is taken high. The analogue output for this

data will be displayed on the scope until the next time WR is taken low and a new value is placedin the internal register.

The keypad can be implemented using the external interrupt 1 line (seekeypad), but not while
http://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypad


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also multiplexing the 7-segment displays. This is because the external interrupt 1 line (P3.3) isalso used by the display decoder (see logic diagram above). Therefore, keypad interrupt andmultiplexing the 7-segment display cannot be used at the same time - the keypad AND gate

should be disabled.

An example of the DAC in action is shown below:

Ramp Generated via DAC Appears on Scope Code for

Ramp

Generatio

n

LED Bank and the

7-segment Displays

Panel

The code that generated the above ramp is also shown (above middle). The DAC's WR input is

taken low permanently (CLR P0.7) while the value in the accumulator is sent to the DAC's

inputs, increased by 8 and then sent to the inputs again, and so on.

When the mouse is placed over the scope screen, a tooltip appears, stating the scope's vertical

scale is one volt per division and the horizontal scale is, in this case, 25 microseconds perdivision. The scope's horizontal scale is tied in with the 8051 system clock frequency (this is

unrealistic, but I feel it's adequate for simulation purposes). If, for example, the system clockfrequency is changed to 11.059 MHz, then the scope's horizontal scale is 17.36 microseconds per

division.


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The LCD Module

As can be seen in the logic diagram below, the LCD Module also shares port 1 with the LEDs

and DAC.

Logic diagram showing the LED bank, DAC and

LCD module connections only.

4-bit Mode: The LCD module is a

simulation of the Hitachi HD44780

and is interfaced to the 8051 in 4-bit

mode. P1.7 through P1.4 are

connected to DB7 through DB4,while P1.3 is connected to the

register-select pin and P1.2 is

connected to the enable pin. Noticethe read-write pin is connected to

ground - the module can only be

written to.

8-bit Mode: By default, as statedabove, the module is interfaced in 4-

bit mode. However, the lower four

data bits (DB3 through DB0) arealso available (on P1.3 throughP1.0). If the user wishes to write to

the module in 8-bit mode, RS and E

should be remapped to other port

pins, using the DIbutton at the topleft of the peripheral panel.

Details of the pin functions and the

instructions for the LCD module are

given below. For details on how to

communicate with the module, seeHD44780.pdfand somesampleprograms.

Reading:Instructions for readingfrom the module have not beenimplemented.
http://www.edsim51.com/8051simulator/HD44780.pdfhttp://www.edsim51.com/8051simulator/HD44780.pdfhttp://www.edsim51.com/examples.html#prog4http://www.edsim51.com/examples.html#prog4http://www.edsim51.com/examples.html#prog4http://www.edsim51.com/examples.html#prog4http://www.edsim51.com/examples.html#prog4http://www.edsim51.com/examples.html#prog4http://www.edsim51.com/8051simulator/HD44780.pdf


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Character Blinking:Because the

simulator does not run in real-time,it would be hard to know if the

module was blinking. Therefore, if

the programmer sets the module to

blinking (seeDisplay on/off controlinstruction below), the cursor

position character alternatesbetween blue text with red

background and red text with blue

background. In this way the

programmer knows at a glance ifthe module is in blinking mode

(when not in blinking mode, all

characters are black with grey

background).


27/44

The enable pin(E, connectedto P1.2) is

negative-edge

triggered. On a

negative-edgeon E, the

module reads

the data linesDB7 - DB4.

4-bit Mode: As

can be seen inthe logic

diagram above,

the module is

interfaced withthe 8051 in 4-

bit mode. In 4-

bit mode, themodule's lines

DB3, DB2,

DB1 and DB0are not used.

The 8-bit

instruction or

data must

therefore besent in two 4-

bit nibbles. Thehigh nibble is

sent first,

followed by thelow nibble.

When the

enable pin is

taken high andthen low, this

causes themodule to read

the pins DB7-DB4 and store

them in either

the IR (if aninstruction is

being sent - ie:


28/44

RS = 0) or theDR (if data isbeing sent - ie:

RS = 1).

Initially, the

module is in 8-bit mode and

must be set to

4-bit mode bythe programmer

before any

other

communications with the

module are

attempted. This

is done bysending the

appropriate

Function Setinstruction (see

instruction set

below).

Why send

Function set

twice? As

stated, themodule is

initially in 8-bitmode,

therefore the

first instructionsent to it is read

as an 8-bit

instruction (as

if DB3 - DB0were in use). If

the correctinstruction is

sent (with DL -on DB4 - set to

zero, indicating

4-bit - seebelow), then

the module


29/44

'knows' it isbeing set to 4-bit operation

and it reads

instructions and

data in two 4-bit nibbles from

then on.

Because itreads the high

nibble first, the

Function set

high nibblemust be sent

again, followed

by the low

nibble.For more

information,

see pages 39and 42 of

HD44780.pdf.

The example onpage 42 is for a

1-line display,

but it

nonetheless

explains clearlyhow to initialise

andcommunicate

with the

module in 4-bitmode.

8-bit Mode:Even if 8-bitmode is being

used,Functionsetmust first be

called to ensurethe module is

set to 2-line

with 5 X8 font.See below.
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2-line, 5 X8Font: The lownibble of

Function set

must be sent

with N = 1(setting the

number of lines

on the displayto 2) and F = 0

(setting the font

to 5 X8 dots).

Function Set

Incorrectly:The

programmermust set themodule to 2-

line, 5 X8

font. Thesimulation of

the HD44780

isimplemented

for 2-line, 5 X8 font only.

However, theprogrammer is

still expected

to write thecode that sets

the module in

this mode. If

the mode isnot set

correctly, an

error message

stating such isdisplayed, as

shown here.

Theprogrammer

must then

reset thesimulator,


31/44

modify thecode and tryagain.

LCD Module Instruction Set

CGRAM


32/44

CGRAM stands for character generator RAM. The module's ROM contains theASCIIcharacterset. For example, the ASCII code for the letter W is 87, so stored in location 87 in the module'sRAM is the pattern for W. This makes it relatively easy to write text to the display. The

following code extract illustrates this point:

MOV A, 'W'CALL sendCharacter ; a subroutine that sends the data in A to the LCD module's

DDRAM

When DDRAM receives a character, the corresponding pattern from ROM is displayed.

Note in the ASCII set, the first seven locations are used for control characters. These charactersare not applicable to the LCD module, therefore these locations are reserved for CGRAM

instead. When a value in the range 0 to 7 is sent to DDRAM, instead of displaying a character

from ROM, the corresponding character from CGRAM is displayed.

This means the user can create eight custom characters. The characters are programmed into

CGRAM by pointing to CGRAM (instead of DDRAM) and then sending data to the module thesame as when sending data to DDRAM.

If you look at the instruction set above you will see there is a Set CGRAM address instruction.

Note the address is six bits in length - we will discuss these six bits shortly.

Also notice there is only one instruction for writing to the module. To write to CGRAM, youmust first ensure the AC (address counter) is pointing to CGRAM. You do this by calling the Set

CGRAM address instruction. As with writing to DDRAM, the AC is incremented (or

decremented, depending on the increment/decrement setting) after each write to CGRAM.

It was mentioned above that ROM contains the ASCII set. This is not altogether true. There are

instances where the character in ROM does not correspond with ASCII. At location 92 youwould expect to see the \ symbol. Instead there is (probably because the HD44780 wasdeveloped in Japan). At location 126, instead of ~ in location 126 there is a right arrow symbol,

followed by a left arrow symbol in location 127.

So, if you want to display the \ symbol, for example, you will first need to create it in CGRAM.You can choose any of the eight CGRAM locations, but let's say we wish to put \ in location 2.

Each character is made up of eight rows, with five dots in each row. You write the pattern for

each row to CGRAM, one row at a time. The row's pattern is made up of 1s where dots are to bevisible and 0s where dots are to be invisible.

The six CGRAM address bits are split into two parts. The top three bits determine which of theeight CGRAM characters is being written to, while the bottom three bits determine which of theeight rows of this character is being written to.

CGRAM Character

Address (binary)Row Address

(binary)Value Written to

CGRAM

010 000 | | | | | 00000B = 00H
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010

010

010

010

010010

010

001

010

011

100

101110

111

| | | | |

| | | | |

| | | | |

| | | | |

| | | | || | | | |

| | | | |

10000B = 10H

01000B = 08H

00100B = 04H

00010B = 02H

00001B = 01H00000B = 00H

00000B = 00H

The three character bits and the three row bits make up the 6-bit CGRAM address.

Note that the top row is row 0 while the bottom row is row 7 (111B). You can use the bottom

row when creating a custom character, but it is not advisable to do so, especially if you intend

using the cursor as well.

The example above shows how to create the \ symbol in CGRAM location 2. You start by setting

CGRAM address to 2, then send the pattern for the character's first row to CGRAM (in this case,00H). The AC will automatically increment to point to the next row. You then send the pattern

for that row (in this case, 10H), and so on for all eight rows.

Once completed, you can then display your new character by setting the DDRAM address to

some value, then send the number 2 to DDRAM and your new character in CGRAM location 2

will appear on the display.

You might then write a test, as shown below, to ensure the correct symbol is displayed when

writing \ to the LCD:

... ; data to be sent to LCD has been placed in ACJNE A, #'\', skip ; if A does not contain \ symbol, skip next line

MOV A, #2 ; replace \ with location of \ in CGRAM

skip: CALL sendCharacter ; call the subroutine that sends the contents of A to theLCD

For complete instructions on how to program the LCD module, seeHD44780.pdf.

The Switch Bank and the ADC
http://www.edsim51.com/8051simulator/HD44780.pdfhttp://www.edsim51.com/8051simulator/HD44780.pdfhttp://www.edsim51.com/8051simulator/HD44780.pdfhttp://www.edsim51.com/8051simulator/HD44780.pdf


34/44

When aswitch is

open a

logic 1

appears

on theport pin

(via thepull-up

resistor)

whileclosing

the

switch

connectsthe pin

directlyto ground

- logic 0.

Theswitch

bank and

theoutputs

of the

ADC are

appliedto port 2.

Therefor

e, it

should benoted

that

when the

ADC is

being

used the

switchesin the

switch

bank

should

all beopen(in

the


35/44

simulator, the

switches

are grey

when

they areclosed).

If aswitch is

closed it

doesn'tmatter

what the

ADC

tries toput on

that line,the line is

held lowbecause

it is

connected directly

to ground

through

theclosed

switch.Logic diagram showing the switch bank and ADC connections only.

The outputs of the ADC are tri-state:

the RD line, which is connected toP3.7, must be low for the ADC

reading to appear on the outputs.

The WR line (connected to P3.6) is

used to initiate a conversion. As it ispositive edge triggered, it must be

taken low and then high to start aconversion.

When the conversion is complete the

INTR line goes low (and remains low

until another conversion is initiated).This line is applied to the external 0

interrupt line, INT0. In this way, the


36/44

8051 can be interrupted by thecompletion of an ADC conversion.

Note the tip that appears when the

mouse is placed over the ADC button.

Clicking on this button disables theADC and enabled the comparator. See

theComparatorfor moreinformation.

Switch Bank and the ADC Panel

The function of the ADC pins are summarised in the following table:

Pin Function

RD Enables the tri-state outputs, when logic 0.

WR On a positive edge, initiates conversion.

INTRGoes to logic 0 when conversion is complete and remains low until anotherconversion is initiated.

i/p Analogue input signal applied here.

CS Enables the device, when logic 0.

D0 -D7

Tri-state digital outputs.

Changing Switch Labels

You can change the label of

a switch in the switch bank

by right-clicking on the

switch and entering a newcharacter.

A switch label can only beone character in length.

The Comparator and the DAC

Many lecturers like to get their students to develop their own ADC using a DAC and a

comparator. To meet this need, the output of the DAC is also applied to the inverting pin of a

comparator, as shown in the logic diagram extract below.
http://www.edsim51.com/simInstructions.html#comparatorhttp://www.edsim51.com/simInstructions.html#comparatorhttp://www.edsim51.com/simInstructions.html#comparatorhttp://www.edsim51.com/simInstructions.html#comparator


37/44

Logic diagram showing the comparator and DAC connections only (notice the ADC is

disabled, therefore its connections to the 8051 are not shown).

The analogue input that is applied to the ADC is also

applied to the non-inverting pin of the comparator, as can

be seen above (in this extract, since the ADC is disabled,

the analogue voltage connection to the ADC is omitted).When the comparator is enabled, the button's label says

Comparator, as can be seen in the image opposite.

Hovering over the button displays a tip - click the buttonto disable the comparator and enable the ADC.

The button corresponds to the switch at the ADC chipselect and the switch between the comparator output and

P3.7 in the logic diagram extract above. You can see the

switch between the comparator output and P3.7 is closed

while at the same time the ADC CS line is switched to+V, disabling the ADC.

Comparator Panel


38/44

When the comparator is enabled it can then be used together with the DAC to implement anADC. There are many techniques that can be used.

Learn about comparators and DACs used as ADCs(An external site that is not affiliated with

EdSim51.)

The Motor

P3.0 and

P3.1 are

applied to adual bridge

driver, the

outputs ofwhich are

applied to a

bi-directionalDC motor.

The truth

table for the

bridge andits effect on

the motor is:

A B motor

0 0 stop

0 1 forward

1 0 reverse

1 1 stop

Logic diagram showing the motor and UART connections only.

In the imageon the left,the motor's

shaft is in the

default

position(pointing at 3
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39/44

o'clock).Notice the

sensor

(depicted by a

vertical line

at the top ofthe motor) is

black.

When the

motor's shaftlines up with

the sensor,

the sensor

changes fromblack to red,

as shown inthe image onthe right.

Motor Panel

The motor sensor, which is applied to P3.5, goes low once every revolution (in the simulator,whenever the motor shaft lines up with the sensor, the sensor changes from black to red and P3.5

goes to logic 0). P3.5 is the external clock source for timer 1. Therefore, code can be written that,

using timer 1, counts the motor's revolutions.

The speed of the motor can be varied manually (using the slider to the right of the motor - take a

look at the hardware screenshots above). This will make the rev. counting programs moreinteresting.

Note: The motor control lines share the TXD and RXD lines for the 8051's internal serial port.As can be seen in the logic diagram extract above, these lines are also connected to the external

UART. Therefore, when exercising the motor, garbage messages may appear in the UART's

receiver window. The function of the external UART is explained below.

The motor can be disabled by clicking on the Motor Enabledbutton. Why would you want to

disable the motor? See The UARTbelow.

The UART


40/44

As stated above, themotor control lines

share the same port

pins as the 8051

serial port RXD and

TXD. An externalUART is connected

to P3.0 and P3.1.

Data received from

the 8051's serialport appears in the

Rxwindow. Thedata in this window

can be cleared at

any time by

clicking the RxResetbutton.

External UART Panel

Data can be transmitted to the 8051's serial port by typing text in the Txwindow and clicking on

the Tx Sendbutton, which initiates transmission. When this button is clicked, the Txwindow's

background colour changes to grey, indicating the window is not editable. The title of the Tx

Sendbutton changes to Tx Reset. Clicking on the button at this point clears the Txwindow. Its

background colour changes back to white - the user can type more text and click Tx Sendto

restart transmission.

The data transmitted by the external UART is terminated with the \rcharacter (theASCIIcodefor \ris 0DH). In other words, when the text abcis transmitted by the UART, the actual data

sent is abc\r(or, in ASCII - 61H 62H 63H 0DH). The UART can also transmit a list of 8-bit

numbers instead of text. SeeHEX in Uartfor more information.

The UART's default Baud rate is 4800. The user can select from a drop-down list of standardBaud rates (as can be seen below). Whenever the Baud rate is changed, the external UART's

receiver and transmitter are reset.

The UART can be set to even parity, odd parity or no parity by clicking on the Paritybutton,

cycling through the three options:No Parity(the default), Odd Parityand Even Parity.

For more information on the 8051 serial port and on adding a parity bit, clickBeginner's Guide

to the 8051 - Serial Port.

When communicating with the UART, the pins P3.0 and P3.1 will therefore be changing value,which will have the side effect of turning the motor. To stop this, the user can click the Motor
http://www.asciitable.com/http://www.asciitable.com/http://www.asciitable.com/http://www.edsim51.com/simInstructions.html#hexInUart2http://www.edsim51.com/simInstructions.html#hexInUart2http://www.edsim51.com/simInstructions.html#hexInUart2http://www.edsim51.com/8051Notes/8051/serial.htmlhttp://www.edsim51.com/8051Notes/8051/serial.htmlhttp://www.edsim51.com/8051Notes/8051/serial.htmlhttp://www.edsim51.com/8051Notes/8051/serial.htmlhttp://www.edsim51.com/8051Notes/8051/serial.htmlhttp://www.edsim51.com/8051Notes/8051/serial.htmlhttp://www.edsim51.com/simInstructions.html#hexInUart2http://www.asciitable.com/


41/44

Enabledbutton which has the effect of disabling the motor (the button's title then changes toMotor Disabledand the motor can be re-enabled by clicking the button again).

UART Transmitting HEX Data

Rather than text, a list of 8-bit numbers(written in HEX) can be transmitted. To

do so, the user encloses the list in curlybraces, each number separated by a

comma, as shown in the image opposite.

When text is transmitted, it is terminated

by 0DH. This is not the case with a list

of numbers. In the example shown

opposite, the four numbers 56, 3a, 23and e7 are transmitted, nothing more.

If the user wishes to send {56, 3a, 23, e7} as text rather than a list of 8-bit numbers, the text isescaped using the \ character. Therefore, \{56, 3a, 23, e7} in the Tx field would result in {56,

3a, 23, e7} followed by 0DH being transmitted to the 8051.

The Keypad


42/44

Logic diagram showing the keypad connections only.

The 4 X3 keypad is interfaced in a standard format, as can be seen in the logic diagram extract

above. All of port 0's pins, except pin 7, are used by the keypad.

External 1 Interrupt: The 3 columns are connected to the inputs of an AND gate, the output of

which is connected to P3.3, the external 1 interrupt pin. The AND gate is disabled (by default)

because this pin (P3.3) is also used by the display-select decoder (seeDisplayabove). To makeuse of the external 1 interrupt with the keypad, make sure the AND gate is enabled. But

remember, you won't be able to multiplex the displays and use keypad interrupts at the

same time. Instead you should use busy-waiting on the keypad.

Key Bounce

If Key Bounceis enabled, as shown in the image

opposite, then the keys will bounce when closed (the

keypad only bounces if thekeypad modeis set tostandard). So the user knows a key is bouncing, its

colour alternates between red (switch open) and dark red

(switch closed). Once the switch finishes bouncing, itscolour reverts to dark grey. The length of the switch

bounce is 30 ms.

Note: a key will only bounce while a program is

running. If the user pauses the running program,

then the switch bounce also pauses.

Notes on interfacing to a keypad:Beginner's Guide to the 8051 - Peripheral Interfacing

Keypad Modes

Next to the keypad is a menu (see image above). This gives the user a choice of three settings for

the type of keypad. By default the keypad mode is set to Standard. The other two types are

Pulseand Radio.

Standard- in standard mode the keys are independent of each other. Any number of

keys can be closed at the same time. A closed key is reopened simply by clicking on it

again.

Pulse- in pulse mode a key is closed while the (left) mouse button is held down. Oncethe mouse button is released the key reopens.

Radio- in radio mode only one key at a time can be closed. For example, if key 5is

pressed (ie: closed) and then key 7is pressed, key 5automatically reopens. As in

standard mode, a closed key is reopened simply by clicking on it again.

When the user switches to another keypad mode, using the adjacent menu, all closed keys are

automatically reopened.
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Changing Key Labels

You can change the labelof a key by right-clicking

on the key and entering a

new character. Key labelscan be any length. The

keypad resizes

automatically.

Saved Settings

The following settings are saved during the simulator shut down process:

Original Setting

Update Freq. 1

Bitfield Address ACC

Data/Code Memory Data Memory

File System Directory Operating System Dependent

ADC/Comparator Enabled ADC Enabled

External UART Parity No Parity

External UART Baud Rate 4800 Baud

Keypad AND Gate Disabled

Keypad Type Standard

Key Bounce No Key Bounce

Key Labels #, 0, *, 9, 8, 7, 6, 5, 4, 3, 2, 1

Switch Labels 0, 1, 2, 3, 4, 5, 6, 7

Motor Enabled/Disabled Enabled

These settings are saved in two files, edsim51diSettings.serand

edsim51diHardwareSettings.ser . The files are (most likely) saved in the same folder as the

edsim51di.jarJAR file on Windows or Mac and in the user's home folder on Linux. When the

simulator is launched it tries to open these file. If the files exist then the information in them isused to restore the system settings to the values they were when the simulator was last shutdown. If the files do not exist or are corrupted in some way, they are ignored and the simulator is

launched with the original settings.
http://www.edsim51.com/simInstructions.html#updateFreqhttp://www.edsim51.com/simInstructions.html#updateFreqhttp://www.edsim51.com/simInstructions.html#bitfieldhttp://www.edsim51.com/simInstructions.html#bitfieldhttp://www.edsim51.com/simInstructions.html#dataCodeMemoryhttp://www.edsim51.com/simInstructions.html#dataCodeMemoryhttp://www.edsim51.com/simInstructions.html#loadSavehttp://www.edsim51.com/simInstructions.html#loadSavehttp://www.edsim51.com/simInstructions.html#switcheshttp://www.edsim51.com/simInstructions.html#switcheshttp://www.edsim51.com/simInstructions.html#uarthttp://www.edsim51.com/simInstructions.html#uarthttp://www.edsim51.com/simInstructions.html#uarthttp://www.edsim51.com/simInstructions.html#uarthttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#switchBouncehttp://www.edsim51.com/simInstructions.html#changingKeyLabelshttp://www.edsim51.com/simInstructions.html#changingKeyLabelshttp://www.edsim51.com/simInstructions.html#changingSwitchLabelshttp://www.edsim51.com/simInstructions.html#motorhttp://www.edsim51.com/simInstructions.html#motorhttp://www.edsim51.com/simInstructions.html#motorhttp://www.edsim51.com/simInstructions.html#changingSwitchLabelshttp://www.edsim51.com/simInstructions.html#changingKeyLabelshttp://www.edsim51.com/simInstructions.html#switchBouncehttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#keypadhttp://www.edsim51.com/simInstructions.html#uarthttp://www.edsim51.com/simInstructions.html#uarthttp://www.edsim51.com/simInstructions.html#switcheshttp://www.edsim51.com/simInstructions.html#loadSavehttp://www.edsim51.com/simInstructions.html#dataCodeMemoryhttp://www.edsim51.com/simInstructions.html#bitfieldhttp://www.edsim51.com/simInstructions.html#updateFreq


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Note:When stepping through or running code, the length of time that passes is not onlyexperiencedby the 8051, but by all the peripherals as well.

If the instruction being executed is a 1 cycle instruction then, with a system clock is 12 MHz, the

length of time passed is 1 us. Therefore, 1 us has passed for the UART and for the ADC and so

on. In other words, if code is not being executed, time has stopped.

If you have questions about the EdSim51 simulator, please visit ourCommentspage.

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