CERL Report X-15

THE PLATO IV

STUDENT TERMINAL

JACK STIFLE

November ,1974

Computer- based Education Research Laboratory

University of Illinois Urbana Illinois

This work was supported in part by the Joint Services Electronics Program (U.S. Army, U.S. Navy, and U.S. Air Force) under Contract DAAB 07-67-C-0199; in part by the Advanced Research Projects Agency under grant ONR Nonr 3985(08); in part by Project Grant NPG-188 under the Nurse Training Act of 1964, Division of Nursing, Public Health Service, U.S. Dept. of Health, Education, and Welfare; and in part by the State of Illinois.

Copyright G) November 1974 by Board of Trustees of the University of Illinois

First Printing Revised Revised

March 1970 June 1973 November 1974

Reproduction in whole or in part is permitted for any purpose of the United States Government.

Distribution of the report is unlimited.

THE PLATO IV STUDENT TERMINAL*!

Jack Stifle

Coordinated Science Laboratory

and

Computer-based Education Research Laboratory

University of Illinois, Urbana, Illinois 61801

ABSTRACT

This report describe5 a graphics terminal des igned for use as

a remote computer input-output terminal. The terminal features a

plasma display panel, self-contained character and line generators

and the ability to communicate over voice grade telephone circuits.

* This work was supported in part by the Join t Services Electronics Program (U . S . Army, U. S . Navy , and U.S. Air Force) under Contract DAAB-07- 67-C-0199.

1This report was originally titled, "A Plasr.1a Display Terminal," \..rhen

published in March, 1970 and Mar ch , 1971 .

TABLE OF CONTENTS

CHAPTER 1 - DESCRIPTION Page

1. 0 INTRODUCTION. • • . . • . • . . • • . . • • • • • • • • • • . . • . . . • . . . • . . • . • 1

1.1 TERMINAL DESCRIPTION. • • • • • • • . . • • • • • • • • • • . . • • • • . . • . • • 4

1. 2 AUXILIARY EQUIPHENT .. ....... .. • • • . • • • • • . • • . • . . • . • . • . 6

CHAPTER 2 - OPERATING HODES

2. 0 HORD FORMAT. . • • • • . • • • . • . . . . • • . • • • • • • • • • • • • • • • • • . • . • . 8

2. 1 CONTROL \vORD. • . • • . • • • • • • • • • • • • • . . • • • . • • • • • • • • • • • • . . • 8

2 . 2 MODE HORD. • . • • • • • . • • • • • • • • • • • • • • • • • • • • • . • • . • • • • • • • • • 12

2.3 HODE 00 ••••••••• • ••• •. • • •.•• ••• ••• .•• • ••• ..•.•..••• . 13

2.4 !'10DE 01 •.••.•••• • .•• •.••• .•.•••.• .• ••••• •••• •••.••.• 13

2 . 5 MODE 10 •..•••••• •. •••••.•••• •. •.•••.•..•.•. • ••••.•.• 13

2 . 6 MODE 11 •..•.•••.• . • • •••••. ••.• ••••• • ••••••....•..•.. 15

2 . 7 CONTROL CHARACTERS .. • • • • • • • • • • . . • • • • . • . • • • . • • • . • . . • . 16

2. 8 ERROR CONTROL. • . . • • • . • . • . • • • . • • • • • . . • • • • • • • • • . . • • • • • 21

CHAPTER 3 - TERMINAL GENERATED DATA

3 . 0 DATA SOURCES. • • • • • • • • • • • • . • . • • • • • • • • • . • • • . • . • . • . . • . • 22

3 . 1 OUTPUT HORD FORMAT . . • . • . . • • . . • • • • • • • • • • • • • • . . . . • . • • • 22

A PLATO IV Student Te rminal

CHAPTER 1 - DESCRIPTI ON

1. 0 I nt roduction

Thi s r e port descr ibes t he student t e r minal ( r emote comp uter

t ermi na l) , desi gne d for use in the PLATO IV compu ter- aided- i nstr uc tion (CAT)

sys tem. Al though the t e rmi na l is intended f or 11se i n teach in~ aopl i ca t i.ons ,

it has manv fea tures 1vhich make it useful i n ma ny other computer terminal

aopl i cat i ons . These features include :

1.

3 . ·

4 .

5 .

6 .

7 .

An R 1/2- inch square plasma displav nanel that i s readnhle in a br ight ly light ed room wi t hou t evestrai n .

Pe rma nent s t or age of i nforma t ion on the clisolav sc r een lvithout f li cker. Absolute l y no r ef r eshing of t he disnlay oanel by the computer i s r equi r ed .

Se l f - cont a ined character and l i ne generator s .

A character writ ing sneed of 180 characte r s per second a ncl t he caoability of displa'!ing 11 0 to 204R characters on t he scr een .

A line dra1ving speed of 60 l ines per sec.ond .

A character re~ertoire of 256 charac t ers , 128 of which a r e alter able via the comou ter nr ogram .

The ability to transmit ~nd receive data on voice grade teleohone circuits .

8 . A ranclom- acccss s l ide projec t or for rear nrojec t ion of static informa t ion on t he disolav sc r een.

9 . Addi t iona l inpu t ~ ou tput channels f or th e con t r ol o f a ux i liar v equ i omen t .

10 . An optiona l random-access audio resoonse unit .

There are th r ee ~eneral requirements which mav he used to char ac t e r ize

a CAl computer ten8i nal .

First , the terMinal must be caoable of servi ng t he needs of a br oad

2

class of relatively unsophisticated users, most of ~Jhom \Jill he encountering

computer ter~inals for the first time. Users might include, for example,

grade school students studying arithmetic or geo~raphy, high school students

studying French or Spanish, and college students studying biolo~y or chemistry.

The terminal must present information to each of these users in a form that

he can readilv understand.

Second, the terminal must be capable of re~ote operation via low grade

telephone lines. This requirement is essential to permit the locating of

terminals in widely separate schools without the need for expensive communi-

cation links.

Third, the terminal should cost less than $5000 to be competitive with

1 the present costs of education.

To meet the first requirement mentioned above, the terminal must have

graphical capability. It must be able to present pictoral information such

as maps, ~raphs, circuit diagrams, anatomical drawings, etc. Some type of

line ~enerator which can be used to generate such objects is thus required.

A very versatile character generator is also required. The terminal

must be capable of displaying not only upper and lower case English alpha-

numeric characters, hut also foreign language characters and any special

symbols which may be unique to a particular suhject under study. Such a

need implies a character generator whose repertoire can be dynamically

altered by the computer.

The need for ~oeration over low grade telephone lines implies a limited

1n. Alpert and D. Bitzer, "Advances in Computer-based Education," Science, Harch 20, 1970, Volume 167, pp. 1582-1590.

3

availab le bandwidth of appr ox i ma t e l y 1200 b i t s / s econd . Such low bandwidth

neces si t ates local s t orage of infor mation with i n the termi nal .

Depending upon the data format used , anywhere from 75K to 250K bi t s of

memo r y may be r equi red to sto r e immages for pres entat i on on a cathode-ray

tube (CRT) with 500 line resolution. A relatively high b andwidth , typically

4.5 ~lliz , i s required between this memory and t he CRT to pr event flicker of

the image . Fas t digital to analog (DA) converters may be requi r ed t o inter-

face the terminal process i ng unit t o the CRT .

ilirect viewing storage t ubes may be used t o over come the flicke r prob l em

but these devices suffer f r om l ow b rightness and t he i n ab i lity to perfor m

selective erase operations on the displayed data.

2 The use of a plasma panel , on the other h and , with i t s inherent

memory , eliminates the refres h memo r y while pr es erving the select i ve e r ase

function . Because each point is stored on the panel as it is displayed ,

the terminal electronics need operate only fast enough t o stay ahead of the

incoming da ta. A panel writing r ate of 30 KHz is adequate fo r this applicat i on .

The digital nature of the plasma panel a lso el i minates the need f o r any DA

converters .

The t hin transparent st r ucture of the pl asma panel permi t s the panel

to be used as a sc reen for the viewing of information in the form o f slides

or microfiche which can be projected on the rear of the panel . Such info rma-

2R . L . Johnson , D. L . Bitzer , and H. G. Slo ttow , ''The Device Characteristics of the Plasma Display Elemen t, " IEEE Tr nnsac t ions on El ectron Devices , Vol. ED- 18 , No . 9 , September 1971, pp. 642- 649.

4

tion can be stored in the terminal and projected on the panel, under computer

control, thus providin~ a presentation of dvnamic computer generated data

superimposed on static (slide) data. This local storage of static informa­

tion reduces the memory required in the central computer and at the same time

results in more efficient use of the communication link.

1.1 Terminal Description

A blocl: diagram of the prototype terminal is sh01vn in Figure 1.0. The

seria l i nput port is designed to accept data arriving at a rate of 1200

bits./second in the fo rm of a freq uency-modulated (fm) signal, which permits

the terminal t o operate on voice grade telephone circuits . The terminal

\vord size is 20 bits and therefore the terminal word rate is 60 \vords per

second. The terminal word format is discussed i n Chapter 2.

The demodulator recovers the data from the fm signal and shifts the

data into the serial input register (SIR). After a full word has been

assembled in the SIR it is transfe rred t o t he Data (D) Register.

The 20-bit D register is the distri~ution center of t he terminal .

From this r egister data may be transferred to a ll i nternal sections of

the terminal as well as any external equioment connected to the t erminal.

The 5 bit mode register 01) is analogous to the instruction reRister

in a digital computer . This register directs the Terminal Control section

in the processinp, of incoming data. Terminal Control provides the timing

and control signals for cont r olling the flow of data \.Jithin the termi nal.

Four modes of operation are ava ilable and are discussed in Chapter 2.

The data is displayed on a Digivue* Plasma Display Panel . This panel

*Trademar~ of Owens- Illinois, Inc.

Voice Grade ------1~ Line .....__---J

(Serial In put)

Voice Grode Line

Character Genera tor

Terminal Control

(Seria l Output)

Figure 1. Terminal Block Diagram

Line Genera tor

Externa l Input

Channe l

Externa I Output

Channel (15 bits)

Slide Proj

DS-1539

6

is a 8 1/2- inch square panel containing 512 addressable points along each

axis or a total of 262 ,144 points. The address of any poin t on the panel

is specified by the contents of the 9 bit X and Y registers. The ou tputs

of these registe rs are sent to the decoding and driving circuits which

drive the displRy panel .

The line generator contains the circuits used in plotting lines on t he

panel . Li nes of any length may be drat.m at the rate of 60 lines per second .

The character generator contains four memories each containing the

points for plotting 64 characters or a total of 256 charac ters. Two of the

memories are read- only memories (ROM) and t\-10 are random access (RN1) .

In the latter case the memories are loaded hy the computer t.Jith special

charac ter or graphical data as required by the terminal user . Characters

are plotted at a rate of 180 per second .

A 64 character keyboard provides the terminal operator with an input

link to t he computer cent er. Data from the keyboard is entered into th e

serial output register (SOR) . From the SOR data is shifted into the

modulator where it is encoded as an fm signal for transmission t o the

compute r center .

Three additional inputs to the SOR are provided . One port permits

Terminal Control to transmit terminal condition information t o the computer

while the other ports provide access to the computer center for externally

conn~cted equipment.

l. 2 Auxiliary EC1 uinmen t

Three 15 bit output channels are provided to permit operation of

exte rnal equipment .

i •

7

One channel is used to transmit data t o a random access slide projector3

\vhich can project slides on the rear of the plasma display panel . The slide

projector will contain a 256 slide memory with an access time of . 2 second .

A second ch;mnel may be used to address an audio response unit. The

audio unit \vill , upon command from the computer center, play hack a messa~e

to the terminal operator . Up to 15 minutes of prerecorded audio messages

4 may be available with an average access time of .5 second.

Other t ypes of equipment which might be at t ached t o the terminal

include printers, or othe r hard copy devices and various t ypes of data

acquisition and recording equipment.

':1 -'D . L. Bitzer, R. L . Johnson, anti D. Skane rdas , "A Digitally Addres sab le

Random- Access ·I mage Selector and Random Access Audio Sys tern," r.ERL Repor t X-13 , Computer- based Education Research Laboratorv, University of Illinois, August , 1970 .

4Ibid .

8

CHAPTER 2 - O?ERATINr. MODES

2 . 0 Hard Format

The data to be processed by the terminal consists of ~0 hit words

with the format shown in Figure 2.0.

19 18 01 no

DATA

Figure 2 .0 Terminal hlord Format

Bit 00

Bits 01 - 18

Bit 19

Paritv hit - even parity

Data

Control bit 0 - 1

control word data ~vord

Terminal ,.,o rds may be of t~.Jo types ; control words and/or data words. Da ta

v.rords (c 1) contain t he data to be processed hv the terminal ~.Jhile con trol

words (c 0) a re instructions used to establish cer tain conditions ~vithin

the t ermina l.

2 . 1 Contro l Word

The control ~wrd format is shown in Figure 2 .1.

19 18 17 16 15

Bits 01 - 15

Bits 16 - 18

01 00

DATA

Figure 2 . 1 Control \.Jord Forma t

Data

Destination of data within the terminal

9

D 000 (NOP)

19 18 17 16 15 01 00

I o I o o o I 0-----·--- --- - ----- - -------- --------------0 I o I This word is a NOP (no- ope r at i on) instruction . The word is input by

the t ermina l but the te rminal condition is not altered in any way .

D 001 (LDM) Load Mode

19 18 1 7 16 15 14 13 07 06 05 01 00

I 0 I 0 0 l I I I ~ I HORD COUNT TI1is instruction loads the Mode r egister (M) with b its 01- 0 5 . In

addition, if bit 14 (WC) is a "1" the i.Jo r d Count r egister will be l oaded

with bits 07- 1 3. The mode is described in Section 2.2 and t he Wo rd

Count in Sec tion 2 . 8 . Re ce ipt of an LD M i nstruction whi le the terminal is in

t he ABORT mode will l oad t he l.Jord Count r egis ter but \vil l not alter t he Hode

r egister. Bit 15 is used t o actuate or inhib it external devi ces at tached t o

the terminal . Receipt of an LDM instruction with bit 15 = 1 will inhibit all

inputs f r om external devi ces . These Devices wi l l remain inhibited until r eceipt

o f an LDH instru ction with b it 15 = 0.

D 010 (LDC) Load Co-ordinat e

19 18 17 16 15 11 1'1 09 01 00

This inst ru c tion loads the X register (bi t 10 = 0) or the Y r egister

(b i t 10 = 1) with bits 01- 09. Bi ts 11- 15 are unused .

u = 011 ( LDE ) Load Ech o

19 18 17 16 15 08 07 01 00

ECHO

10

This ins truc t ion l oads the terminal output reRister (SOR) with bits

01-07 . This word is then transmitted back to the computer center.

Programming Note : This instruction should not be sent to the terminal

at a rate greater than once every 32 words . (Once everv 64 words if external

input devices are present at the terminal . ) Exceeding this rate may cause

erroneous data t o be returned to the compute r center.

D 100 (LDA) Load Nemory Address

19 18 17 16 15 11 10 01 00

or00j MEt·IORY ADDRESS

This instruction loads the Memory Address Register (MAR) with hi t s

01-10. Bits 11- 15 are unused. This data word specifies the first storage

address to be used upon entry in t o a Mode 2 operation .

D = 101 (SSL) Load Sli de

19 18 17 16 15 11 10 09 08 05 04 01 00

X y

This instruction is used to operate the slide projector. Bits 01-08

select one of 256 slides for disp lay on the pl asma panel . Bit 09 cont r ols

the projec t or s hut ter . For normal onerati on this bit is al\vavs " 0".

However, if this hit is a "1" , the shutter 1vil l he closed and remain c l osed

unt i l re7eipt of a load slide command with bit 09 = "0". Bit 10 controls

the projector lanp. The lamp ~.Ji ll be turned on if bit 10 is a "1" and off

if bit 10 is a "0".

11

D = 110 (AUD) Load Audio

19 18 17 16 15 01 00

Ia j1 1 AUDIO DATA

This instruc t ion is used to control the audio response unit. The

audio response uni t requires tHo of these ins truc tions pe r audio operation.

The formats of each of these instructions i s described beloH.

15 14 13 12

TRACK

Bits 01 - 12

Bits l3 - 14

Bit 1,5

15 14 08

I I O------ - ------------O I Bits 01 - 07

Bi t s 08 - 14

Bit 1 5

06 OS 01

~- SECTOR

07

Fi rst audio instruction

Specify the message starting address ; bi t s 01 - 05 soecify one of 32 sectors and bits 06 - 12 one of 128 tracks .

Snecify playback or erase as fo l1o•vs :

00 - do no t hing 01 play message 10 - do nothing 11 - record message

A1•Jays " 1". Identi fies fi rst of two audio i ns tructi ons .

HESSAI.E LENGTH IN SECTORS

01 Second audio i nstruction

Snecifv le ng t h of message in terms of sec t ors . One sector equals ~ 1/3 seconds .

Unused

Ah1avs "O" - identifies second audio instrucLion .

12

D 111 (EXT) Load External Channel

19 18 17 16 15 01 00

EXTERNAL DATA

This instruction transfe r s bits 01 - 15 t o a ny equipment a ttached to

the external output channel of the terminal.

2 . 2 Mode Hord

For each mode of terminal operation there i s an associa t ed mode \v<-'rd

which directs the terminal processing of incomin~ data. Once placed in

any given mode the terminal r emains i n tha t mode until r eceip t of a ne\v

LDi instruc tion. The mode word forma t is sh mo~n in Fi~ure 2. 2

05

Bit 01

Bits 02 - OJ

W/E 1

X

0

1

0

1

1

Bits 04 - 05

04 OJ 02 01

s

Figure 2 . 2 Mode 11orrl Format

Sc~een Command . If this bi t is a "1", t he entire display panel is erased a t the time the Mode !Jord is loaded into the t regis ter .

Selec t write'o r erase f unction as follmvs :

Erase

I.Jrite

Write; s uppress all background erase ope r a t ions . This operation is described in more detail i n Sec tion 2 . 6 .

Specify ope r a ting mode

13

2 . 3 Mode 00

Mode 0 is a ooint plotting mode. Each mode 0 data \vord (Figure 2.3)

specifies the address of a point on the panel to he written or er~sed . The

H/E0 bit in the mode word detennines \vhich operation i.s perf ormed.

19 18 10 09 01 00

X y

Figure 2 .3 t-bde 0 Data \vord

·2 .4 Mode 01

Mode 1 i s a line drawing mode. Each data word, Figure 2.4, specifies

the terminal coordinate s of a line , the origin of which is ccntained in the

X and Y registers.

19 18

X. 1

lQ 09

figure 2 . 4 Mod e 1 Data format

Y. 1

01 00

The terminal point of a Riven line is also interpre t e d as the ori?.in

of the next line . Line origins may be reloca t ed, however, hv the use of

the LDC command 1vi thou 1.: exiting from Node 01.

An example of a node 01 operation is s hmvn in Fi.p,ure 2 . 5.

2.5 "1ode 10

Mode 2 is a load tenninal memory mode . Each mode 2 data \vord (Figure

2 . 6) contains a 16 bit word to be stored in the memory location specified

by the presen t contents of the memory address register (MAR) . Up to 1024

16 hit 1vords may be s tored in the terminal. After the da ta has been stored

14

19 18 17 16 15 11 10 09 01 00

f•

DISPLAY

DATA

. Figure 2 . 5 Mode 01 Example

15

19 18 17 16 01 00

HEt10RY DATA ~lORD

Fi gure 2 . 6 t-bde 2 Da t a {Jord

the MAR is au t omatically i nc r emented hy l. Thus , data may be s t o red

sequentiallv i n memory by t ransmitting only Uode 2 da t a Hor ds . The c on t ents

of t he t·1AR mav he chanp,ed at anv time v ia the LDA ins t ruction .

The data , when displayed on the pane l , a npear s as a vert i cal co l umn

wi th bit 01 a t t he bo ttom and hi t 16 a t the t op . The s t o red data i s

di s p l ave d via Nod e 3 wh i ch is des cr ibed in the next sec t i on .

2 . 6 Hode 11

lode J i s a cha r ac t e r pl o tting rrwde . The da t a Hords in this mode

contain three 6 b i t ch a r a c t er codes as s hoiVn i n Fi gure 2 . 7 .

19 18 13 1 2 07 06 01 00

11 I CHAR 1 Cl!AR 2 Cl! AR 3

Fi gur e 2 . 7 Mode J Data lJord

Four 64 charac t e r memories a r e provi ded in t he t e rmi na l. r-Emor i es t10

a nd M1 .a r e read- only memories ( RON ) which con tain the cha r a c ters s hm·.rn in

Tab l e 2 . 1. Memor ies t l ') and tl l

are ra ndom access memories (JW1)' each con-

taining 512 X 16 hit \vo r ds , t he conte nts of \vhich a r e loaded v i a Jl1ode 2 .

The con t en t s of _112 and "13

a re processed hv ~1ode OJ as 64 a rravs of 8 x 16

bit s each . The conte nts of. 8 consecutive addr esses a re disn l ayed as one

cha r ac t e r . All cha r ac t ers are dis plaved wit hin an R x 16 l'1~ trix as shO\m

i n Figure 2 . R. The t op thre e and t he bo ttom r ows oE t he ma trices fo r a l l

cha r acte r s f r om M0 and M1

are alwavs unfi l l ed .

•

16

Figure 2 . 8 Char ac t er ~1atrix

Character write/erase is cont r olled hv the ~rite/erase bits in the

mode word. If H/E0 = 1, cha r ac t e rs are Hritten ; if H/E0

= 0, cha r ac ters are

erased . If W/E1

= 0, the background or normallv unf illed portion of each

character matrix will be erase d, if H/E1

= 1 the backgr ound remains unaltered .

Up t o 32 lines of 64 characters each may be pl o tted for a to t al of

2048 characters . I n comp a r ison, a t ypi ca l page of double spaced tvpe

consis ts of 27 lines of 72 char ac ters or a t o t a l of 1944 characters .

2 . 7 Control Characters

The "uncover' ' code ( 77) is us ed t o gain access t o 12 control characte r s .

These characters are useful in cont rollin~ disn l ay fo rma t i n Mode 3 opera tions .

Upon receipt of a 77 code , the termina l interpre t s the nex t characte r

code as a control char acter r a the r t han a memorv add r ess . Follm.,ring , execu tion of the control charac t e r normal Hode 3 oper a t ions are res ume d. A

descript i on of each control fu nc t ion i s p,iven belm.t .

!

'ADDRESS (OCTAL)

0

1

2

3

4

5

6

7

~0

11

12

13

14

15

16

17

20

21

22

23

24

25

26

27

30

31

32

33

34

35

36

37

110 CHAR

:

a

b

c

d '

e

f

g

h

i

j

k

1

m

n

0

p

q

r

s

t ·

u

v

w

X ·

y

z

0

1

2

3

4

Ml CHAR

iF

A

B

c D

E

F

G

H .

I

J

K

L

M

N

0

p

Q

R

s T

u v w X

y

z -.. ~

.. ...

.

17

'ADDRESS (OCTAL)

40

41

42

43

: 44

45

46

47

50

51

52

53

54

55

56

57

60

61

62

63

64

65

66

67

70

71

72

73

74

75

76

77

MO CHAR

5

6

7

8

9

+ -

* I (

)

$

=

SP

' . . [

]

%

X

¢:

I

" I . ;

<

>

-?

~

..

UNCOVER

Tabl e 2 .1 Cha r acter Codes

Ml CHAR

t

+

+ +

"" 1:

fl

u

n

{

}

& , SP

I 0

-a

e 6

A.

~

tr

p

a

w

~

~

9

@

\ UNCOVER

18

Uncove r ( 77)

This code inst ructs the terminal t o obey the next char acter address as a -.

control f unction . If several un cove r codes a re sent in sequence, the first

non-uncover code wi l l b e treated as the con trol character .

3ackspace (10)

This char ac t er de c r eases by 8 the panel x address, i.e. , moves one

character position to t he lef t . A backspace over a displayed char ac ter does

no t erase the character.

Tab (ll)

This character increases by 8 the panel x address, i.e., moves one

cha r ac ter position to the right. A tab over a disp l ayed character does not

erase the charac t er .

Line Feed (12)

This character decreases by 16 the panel y address, i.e . , moves down one

ch ~ rac ter position . A line fe ed ove r a displayed character does not e rase the

charac t er .

Ve r L i c~ l Tab ( 13)

Th i s character inc reases by 16 the panel y add ress, i.e. , Moves up one

ch arac t e r position . A vertical tab over a displayed charac ter does not e rase

the charac t e r.

Fo rm Feed ( 14)

This character sets the panel address to the upper left corner (x = 0,

y :..: 496) . This is t he firs t character position on the t op line of the display.

No displayed data is erased i n th i s operation.

Carria ge Re turn (1 5)

Thi s cha rac ter cl~a rs (sets to 0) the panel x address and decreases by

16 th e y address. The ~sc reen address is t huti set to the first cha r ac ter

pos i Li o n nit t he line immediately belo\¥ the present line . Ho dis played

19

da t a is e r ased in t his oper a tion .

Supe r script (16 )

This char ac t er i ncreases the panel v address by 5 . Al l characters

received fo l lowing t his code appear as sh01-m in Figure 2 . 9 . This selec t ion

may be r emoved by r ec e i p t of a s ubscr ip t (17) code . No da t a is e r ased i n a

s uhs cript ope r a tion .

-~

! I

Figur e 2 . 9 Supersc r ipt Operation

Subscr ipt (17)

This characte r decreases by 5 the pane l v add r ess . All char ac t e r s

recei ved followi ng th is code appear as sh01m in Figure 2 . 9 . 1. Thi s

c ha racte r may be used to r emove a s uperscrip t se le c tion (16) and t he s upe r -

script code may be used to remove this se lecti on. No da t a i s e r aseci ir1 ,,

s upe r script operation .

•

20

II I lllll~

~

-~ ~

I i I

Figure 2.9 . 1 Subscrip t Operation

Se lec t M0

(20)

This code se l ects character memory 0. All succeeding characters t~ il l

be read from t he memory until receipt of a different memory select code .

Select M1

(21)

This code selects charac t e r memory 1. All succeedi ng characters wil l

be read from this memory unti l receipt of a di f ferent memorv se]ect code .

Select M2 (22)

This code selects charac te r memor y 2. All succeeding characters

will be read from tnis memory until receipt of a different memory select code.

Select M3

(23)

This code selects cha rac ter memnr y 3. All succeedin~ characters will

be read from this memory until receipt of a different memory select code .

•

21

2.8 Error Control

Contained 1 .. ri thin the terminal is a 7 bit Hord Count (IVC) register,

1vhich maintains a record of the nul'lher of non- NOP lvords received bv the

terminal. Ea ch time a non- HOP I·JOrd js tnm sferred i nto the terminal the

Word Count is incremented by 1 .

Upon receipt o f a lvord 11ith a parity e rror the teminal enters the

ABORT mode of operation . In this mode the terminal transmits the con tents

of the t-IC to the computer . The HC 111i 11 contain the a ddress of th e 1110 rd

containing the error.

Once in the ABORT mode the terminal Hi.ll ' refuse to accept any fu rther

information except for a LDM instruction ¥Tith bit 14 a " 1". Receipt of

this 1vord· lvill clear tl1e ABORT Rode and return ti-Je terminal to normal

operation. This met ~od · of error c onL~ol prevents the terminal from

processi.n ;; da ta i:1 th e wr ong mod e .i n the event an e rroneous mode lv o r d i s

r eceived .

22

CHAPTER 3 - TERMINAL GENERATED DATA

3.0 Data Sour ces

Data may be gene r a ted by any of four sour ces wi t hin the terminal or

by an external device connected to the external input channe~ . Internal

sources of data are :

1. A 64 key keyboard shown in Figure 3 . 0 with the coding shovn

in Figure 3.1.

2 . The echo ce de. See LDE inst ruction in Section 2 .1.

, ~ . The Wo rd Count register. See Section 2 . 8 .

4. The Touch Panel . This is an optical i nput device which

permits the t erminal operator to enter data i nto the

computer by poin t ing at areas of olasma pane l with his

f inger .

3. 1 Ou tout \.Jord Format

The data transmit ted f r om the t ermina l consis t s of 11 bit "YTords \vith

the forma t shmvn in Figur e 3 .2.

10 09 08 01 00

I DATA

Fi gure 3. 2 Output llord Format

Bit 00 Parity bit - even parity

Bits 01 - 08 Dn t a Field

Bits 09 - 10 Identity source of data

• I.

23

'\

054 000 001

056 002 003

161 167 004 005 006

145 162 164 171 007 010

165 011

151 133 020

157 160 021 022 033

063 064 065 074

DDDDDDDDDDDDDDDD 014 016 121 127 10 5 122 124 131 125

055 057 141 163 144 146 147 150 152 111

153 117 120

154 174 023

066 024

067 025 034

070 075

DDDDDDDDDDDDDDDD 015 017 101 123 104 106 107 110 112 113 114 134 026 027

053 052 . 172 170 143 166 142 156 155 177 176 175

~DBDDDDDDDDDDB 013 012 132 130 103 126 102 116 l15 137 136 135

140

[ l 100

NOTE: l. Each key h as two diffe r ent inputs. Th.e octal number below the box is the input '"hen :1 key is pressed singly (normal state), and the number above the box i s th e input lvhen the "Shift" key is held down as a key is pressed (shift state).

TI1e "Shift" key alone does not initiate input data transfer, but merely causes an addition of 040 (octal) to a normal input.

2. There is a total of 124 . different inputs.

3 . The input codes 036, 037 , 076, and 077 are not used.

Figure 3.1 Keyboard Coding

..

030 035 071 072

DO 031 032

25

The word fo rmats for each of the input sources is descr ibed below :

10 09 08 0 7 01 00

I 0 0 I 0 I I(EYBOARD DATA I p I 10 09 08 07

10 09 08

TOUCI! X

10 09 08

ECIIO CODE

OS 04

PANEL y

11 0 I EXTERNAL DATA

10 09 08

11 1 I 0 I !<ORO COUNT

10 09 08

01 00

01 00

01 00

01 00

h'he r e several terminals (up to 32) shar e a common l ink to the compute r

center the dr1ta is s e nt t o a multiplexor \vh i ch assigns a tennina l identity

code and adjusts the parity bit befor e transmit ting the data on t o t he

cente r. Tn thLs case , the data has the fo rmat s hm•n in Figure 3. '3 . Except

fo r the iden tity code , bit assig nments a r e the s ame as i n Figur e 3. 2 .

15

TEIUHNAL [OE:JTITY

11 10

DATA

Figure 3 . 3 Hultiplexed \Jo r d format

01 00