A graphics terminal for a digital computer.

University of Windsor University of Windsor

Scholarship at UWindsor

Scholarship at UWindsor

Electronic Theses and Dissertations Theses, Dissertations, and Major Papers

1-1-1971

A graphics terminal for a digital computer.

A graphics terminal for a digital computer.

Frederick Wayne Bristow University of Windsor

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Bristow, Frederick Wayne, "A graphics terminal for a digital computer." (1971). Electronic Theses and Dissertations. 6666.

https://scholar.uwindsor.ca/etd/6666

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by

FREDERICK MAINE BRISTOW

A T h e sis

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F u lfillm e n t o f th e Requirement f o r th e Degree o f M aster o f A p p lied S c ie n c e a t th e

U n iv e r s it y o f Windsor

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1

ABSTRACT

T h is t h e s i s d e s c r ib e s th e l o g i c a l d e s ig n and im p lem en tation o f

a d o t g en era to r and i n t e n s i t y c i r c u i t fo r a computer g r a p h ic s te r m in a l.

A lso a p ro p o sa l fo r a v e c to r g en era to r i s g iv e n a s im p lem en tation was

not s u c c e s s f u lly c a r r ie d o u t.

B a s ic a lly th e d o t g en era to r a llo w s one t o draw d o tte d l i n e s o f

v a r io u s le n g t h s a t v a r io u s a n g le s on a cathode ray tu b e . The d o ts are

g en era ted by u sin g an up/down cou nter i n c o n ju n c tio n w ith a d i g i t a l t o

analog co n v e rter fo r th e v e r t i c a l and h o r iz o n ta l d e f l e c t i o n o f th e beam.

Unblanking p u lse s a re th e n a p p lie d t o th e Z -a x is t o i n t e n s i f y th e d o t s .

The i n t e n s i t y c i r c u i t p ro v id es f m v p o s s ib le i n t e n s i t i e s , dim,

normal, b r ig h t or b lan k ed . When th e d o t, Alphanumeric or v e c t o r g en er­

a to r s a re bein g used , any o f th e fo u r p o s s ib le i n t e n s i t i e s can be ch o sen .

I n th e alphanum eric mode th r e e a d d it io n a l i n t e n s i t y l e v e l s a re automat­

i c a l l y s e le c t e d f o r th e u se r , t o compensate f o r th e v a r ia t io n i n in t e n ­

s i t y which occurs when e it h e r th e la r g e , normal or sm a ll s i z e c h a r a c te r s

are bein g g en era ted .

The proposed v e c to r g en era to r i s e s s e n t i a l l y two in t e g r a t o r s ;

one f o r th e v e r t i c a l and one f o r th e h o r iz o n ta l d e f l e c t i o n . During one

in t e g r a t io n tim e a l i n e o f any le n g th and a t any a n g le co u ld be drawn.

T h is, u n lik e most sy stem s, has th e advantage t h a t a v e c t o r th e f u l l

le n g th o f th e sc r e e n co u ld be drawn i n one i n t e g r a t io n tim e .

i i i

The author w ish e s t o e x p r e ss h i s a p p r e c ia tio n t o

Dr. P.A .V . Thomas f o r h i s s u p e r v is io n and s u g g e s tio n s . Ack­

nowledgement must a l s o go t o th e N a tio n a l R esearch C ouncil

TABLE OF CONTENTS

Page

ABSTRACT i i i

ACKNOWLEDGEMENTS i v

TABLE OF CONTENTS v

LIST OF TABLES v i i

LIST OF ILLUSTRATIONS v i i i

Chapter

I INTRODUCTION

t . i D e s i r a b i l i t y o f a Cathode Ray Tube D is p la y 1

1 ,2 G eneral A sp ects o f th e Problem 2

I I THE DOT GENERATOR

2 .1 In tr o d u c tio n ^

2 .2 Im plem entation 8

2 . 3 R e su lts and C on clu sion s 12

I I I THE INTENSITY CIRCUITS

3 .1 In tr o d u c tio n 15

3 .2 I n t e n s i t y S e le c t io n 15

3*3 P u lse A m p lifier

(1 ) Dot and A/N P u lse A m p lifier 22

(2 ) V ector P u lse A m p lifie r Zk

3 A R e su lts and C onclusion s 26

IV THE VECTOR GENERATOR

^ .1 In tr o d u c tio n 28

v

4 . 3 R e su lts and C onclu sions

V GENERAL CONCLUSIONS

APPENDIX - I LOGIC NOTATION

REFERENCES

LIST OF TABLES

T able Page

1 I d e n t i f i c a t i o n o f B i t P o s it io n s 19

2 Sw itch O peration 36

v i i

1 D isplacem ent o f D ots 6

2 Data and I n s t r u c t io n Word C o n fig u ra tio n 7

3 B lo ck Diagram o f Dot Generator 9

4 Dot Generator ₁₀

5 D em onstration o f Dot Generator O peration 13

6 I n t e n s i t y C ontrol C ir c u itr y 17

7 Dot and A/N P u lse A m p lifier 23

8 V ector P u lse A m p lifier 25

9 B in ary Rate M u ltip lie r 29

10 B in ary Rate M u ltip lie r Output 30

11 V ector C ontrol C ir c u it 33

12 Analog C ir c u it 35

13 Sw itch Timing 37

14 V ector Generator 41

15 I n te g r a to r O peration (0 t o -5V ) 43

16 I n te g r a to r O peration (0 t o 0.8V) 44

17 I n te g r a to r O peration ( - 0 . 8 t o -5V) 4 5

18 Output o f Hold #2 C ir c u it 46

19 Sw itch T ra n sien t Response T est C ir c u it 48

20 T ra n sien t Response T e st R e su lts 52

CHAPTER I

INTRODUCTION

1 .1 D e s i r a b i l i t y o f a Cathode Ray Tube D is p la y

With th e broadening use o f h ig h speed com puters, a need has

a r is e n f o r a f a s t and f l e x i b l e means o f o u tp u ttin g in fo r m a tio n from th e

(1 2 ) ( 1J-)

computer* As a r e s u l t many good alphanum eric g en era to rs which out­

put d ata on a cathode ra y tu b e (CRT) a t a h ig h r a te o f speed have b een

develop ed and a re b ein g s u c c e s s f u lly used when a hard copy o f th e t e x t

output from th e computer i s not req u ired * The alphanum eric g en era to r i s

l im it e d , however, b y th e f a c t t h a t i t can o n ly produce alphanum eric

t e x t , and th u s i t does n ot f i l l t h e needs o f many o f t o d a y 's computer

u s e r s •

A te r m in a l which i s much more i n demand i s a g r a p h ic s te r m in a l

which h as alphanumeric t e x t producing f a c i l i t i e s . Such a te r m in a l a llo w s

th e u ser t o view a g ra p h ic d is p la y on a CRT and a llo w s him t o in t e r a c t

d i r e c t l y w ith th e computer v ia l i g h t b u tto n s, p h y s ic a l sw itc h e s or a l i g h t

pen. T his ty p e o f te r m in a l i s o f g r e a t i n t e r e s t t o th e tim e-sh a red com­

puter u se r s f o r i t g iv e s each u se r th e i l l u s i o n o f b ein g th e s o le u ser o f

th e machine and a t th e same tim e p erm its him t o d i r e c t or m odify th e com-(13)

p u ta tio n p r o c ess from a remote te r m in a l. A g r a p h ic s te r m in a l i s a l s o

o f g r e a t u se i n th e f i e l d s o f computer aid ed d e s ig n , computer aid ed i n ­

s t r u c t io n , data a n a ly s is and p r o c ess c o n tr o l, b ecau se i t p ro v id es f o r

sim p le man-machine in t e r a c t i o n .

As a te a c h in g a id , computer g ra p h ics te r m in a ls a re i d e a l . A t e a ­

cher can program a s e r i e s o f problems i n t o a computer and have them d i s ­

p la y ed on a g r a p h ic s te r m in a l where a stu d en t can attem p t t o s o lv e them .

1

I n th e f i e l d o f computer a id ed d e s ig n , such a te r m in a l a llo w s

fo r th e q u ick d is p la y o f c h a r ts and graph s, a s w e ll as p i c t o r i a l diagram s,

which a re o f g r e a t v a lu e t o th e d e s ig n e n g in e e r . A gain th e fe a tu r e o f

such a system i s th e e a se by which man-machine i n t e r a c t i o n can be accom?*

p lis h e d . I t i s through t h i s in t e r a c t i o n t h a t d e s ig n changes can be d i s ­

p layed q u ic k ly on a CRT w ith o u t h o ld in g up th e en g in eer or computer, l i k e

a co n v e n tio n a l l i n e p r in te r or p l o t t e r . Thus we see t h a t a g ra p h ics t e r ­

m inal i s a must f o r many computer u s e r s , and i t th e r e fo r e w arrants th e

tim e and e f f o r t sp en t i n tr y in g t o d ev elo p a good and econom ical g r a p h ic s

te r m in a l. An attem p t was made t o d e s ig n l i n e g e n e ra to rs f o r a g ra p h ics

te r m in a l th a t were more econom ical th a n th o s e c u r r e n tly a v a i l a b l e .

1 ,2 General A sp ects o f th e Problem

Sin ce r e se a r c h had b een c a r r ie d out i n th e f i e l d o f CRT d is p la y s

(

) (

)

i n th e E l e c t r i c a l E ngineering Department a t th e U n iv e r s it y o f Windsor

i t was d ecid ed t h a t work should be done t o in c r e a s e th e c a p a b i l i t i e s o f th e

computer te r m in a l t h a t was b e in g d ev elo p ed . I t was f e l t t h a t th e a rea o f

t h i s r ese a rc h sh ou ld be computer g r a p h ic s , and a s a r e s u l t i t was d ecid ed

t h a t a d o t and v e c t o r g e n e ra to r, a s w e ll as an i n t e n s i t y c o n tr o l c i r c u i t ,

should be d esig n ed and im plem ented.

The d o t g en era to r was t o be d e sig n e d so t h a t i t could be used

i n a r e l a t i v e , r a th e r th an an a b s o lu te mode. That i s , when c o n tr o l i s

t r a n s fe r r e d t o th e d o t g e n e r a to r , d o tte d l i n e s co u ld be drawn o n ly from

th e p la c e where th e e le c t r o n beam had b een p o s itio n e d j u s t p rev io u s t o

3

i n i t i a l l y , u sin g th e v e c to r g e n e r a to r . T h is d is c u s s io n o f th e d o t gener­

a to r w i l l be con tin u ed i n th e n ext c h a p ter .

When th e p r o je c t was begun, th e i n t e n s i f i c a t i o n o f th e beam was

b ein g ach iev ed by u sin g a H ew lett Packard vacuum tu b e a m p lifie r which

a llo w e d o n ly one i n t e n s i t y f o r th e d is p l a y . I t was f e l t t h a t t h i s was

n o t f l e x i b l e enough a s i t was d e s ir a b le t o have th e c a p a b il it y o f drawing

c h a r a c te r s a t th r e e d i f f e r e n t b r ig h tn e s s l e v e l s , a s w e ll a s having a

blanked mode which would a llo w f o r p o s it io n in g th e beam. However, t h i s

s t i l l d id not a llo w enough f l e x i b i l i t y , a s i n th e A/N mode a problem

a r o se when v a r io u s s i z e c h a r a cter s were drawn, s in c e th e A/N g en era to r

m erely in c r e a s e s or d e c r e a se s th e s i z e o f th e d o t m a trix used t o g en era te

c h a r a c t e r s . T h is n a t u r a lly l e d t o th e problem o f in c o n s is t e n t c h a r a cter

i n t e n s i f i c a t i o n a s th e ch a r a cter s i z e v a r ie d . When sm a ll l e t t e r s were

drawn, th e y appeared b r ig h t e r th a n th e normal s i z e c h a r a c te r s, due t o

th e in c r e a se d packing d e n s it y o f th e d o t s . S im ila r ly , when la r g e l e t t e r s

were drawn, th e y appeared d u l l , due t o d ecrea sed packing d e n s it y . Thus,

compensating i n t e n s i t y l e v e l s had t o be in co rp o ra ted i n t o th e i n t e n s i t y

s e l e c t i o n c i r c u i t s ; however, a com plete d is c u s s io n o f t h i s w i l l be de­

f e r r e d u n t i l Chapter 3»

The t h ir d p art o f th e p r o je c t in v o lv e d th e d e s ig n and implement­

a t i o n o f a v e c to r g e n e r a to r . T h is g en era to r would g iv e th e te r m in a l th e

c a p a c ity o f drawing b la n k , s o l i d or dashed l i n e s o f any le n g th and a t

any a n g le on th e CRT. T h is would th e n g iv e th e d e s ir a b le a b i l i t y t o

draw graphs, p l o t s or o th er o b j e c t s . VB.th th e a id o f so ftw a r e , t h i s gen­

e r a to r cou ld be made t o draw c i r c l e s and s e c t o r s . A more com prehensive

d is c u s s io n o f th e d e s ig n and su c c e ss o f t h i s s e c t i o n o f th e p r o je c t w i l l

be g iv e n i n Chapter

CHAPTER I I

The Dot Generator

2 .1 In tr o d u c tio n

I n order t o save co re space and t o in c r e a s e th e r e f r e s h

speed o f th e d is p la y , th e core c i r c u i t r y was d e sig n e d i n such a way

t h a t once a DOT, A/K orVECTOR i n s t r u c t io n i s decoded, a l l th e

forthcom ing output from th e core i s co n sid ered data t o th e d e sig n a te d

g e n e r a to r . T his p ro cess o f o u tp u ttin g d ata t o th e s p e c if ie d gener­

a to r c o n tin u e s u n t i l a new in s t r u c t io n i s en cou n tered . At t h i s tim e

th e g en era to r p r e v io u s ly b ein g used i s turned o f f and th e co re output

i s d ir e c t e d t o th e most r e c e n t ly s p e c i f i e d g e n e r a to r .

A second fa c t o r t h a t had t o be co n sid ered i n th e d e s ig n o f

th e d o t g en era to r was th e spacing o f th e d o ts on th e s c r e e n . T his

spacing i s determ ined by th e le n g th o f th e r e g i s t e r s used i n con­

ju n c tio n w ith th e D/A c o n v e r t e r s . I n t h i s p a r tic u la r c a s e , a 10 b i t

10

r e g i s t e r was used which a llo w s fo r 2 = 1024 d i s t i n c t p o s it io n s along

each a x i s . I f a 10 in c h square sc r e e n were u sed, th e r a s t e r u n it

10

would be 1024 £* .0 1 in c h . Thus when an i n s t r u c t i o n t o increm ent

i n th e I ' s p o s it io n i s g iv e n t o th e d o t g e n e ra to r, d o ts would be

placed on th e sc r e e n i n .0 1 in c h in crem en ts. P r o v isio n was a l s o made

so t h a t d o ts can be p la ced a t ev ery second or ev ery fo u r th r a s t e r

1 1

p o s it io n , th u s a llo w in g d o ts t o be p la ced a t 50 or 25 in c h i n t e r ­

v a l s , r e s p e c t iv e ly , on th e s c r e e n . Furtherm ore, p r o v is io n was made

t o g en era te a s e r i e s o f d o ts i n th e same d i r e c t i o n u sin g th e same

5

Figure iA i s an example o f a X which i s an increm ent X i n th e

4 ' s p o s it io n w ith a r e p e t i t i o n o f 1. Thus a s in g le d o t i s g en era ted

which i s placed ^ r a s te r u n it s i n th e p o s i t i v e X d ir e c t io n from th e

o r ig in a l p o s it io n o f th e beam. A s in g le decrement i n th e I I ' s po­

s i t i o n i s shown i n Figure IB. Here th e d o t i s p la ced 1 r a s t e r u n it i n

th e n e g a tiv e Y d ir e c t io n from th e o r ig in a l beam p o s i t i o n . A combined

disp lacem en t i n th e X and I d ir e c t io n , a s w e ll as a r e p e t i t i o n o f 2 , i s

shown i n Figure 1C. I n t h i s c a se th e f i r s t d o t i s d is p la c e d 2 r a s t e r

u n its i n th e p o s i t i v e X d ir e c t io n and ^ r a s t e r u n its i n th e p o s i t i v e Y

d i r e c t i o n from th e o r ig in a l beam p o s it io n . The second d o t i s p la ced 2

r a s t e r u n it s i n th e p o s i t i v e X d ir e c t io n and 4 r a s t e r u n it s i n th e p o s i­

t i v e Y d ir e c t io n from th e f i r s t d o t.

B efore an e x p la n a tio n o f th e c i r c u i t i s begun, a b r i e f exp lan ­

a t io n o f th e word format w i l l be g iv e n . Figure 2 shows th e b i t c o n fig ­

u r a tio n f o r both th e i n s t r u c t io n and th e d ata words. From th e diagram

i t i s seen th a t whenever a code 42xx i s encountered, th e dot g en era to r

i s i n i t i a t e d . The l a s t two b i t s o f th e in s t r u c t io n word are used fo r

i n t e n s i t y c o n tr o l and w i l l th e r e fo r e be d is c u s s e d i n th e next c h a p te r .

The d ata word c o n ta in s a l l th e in fo rm a tio n fo r c o n t r o llin g th e d o t g en ­

e r a t o r . B it s 2 through 5 i n c l u s i v e l y , c o n ta in th e number o f dot segments

t o be g e n e ra ted . B it 6 in d ic a t e s i f th e X counter i s t o be increm ented

or decrem ented, and b i t s 7 and 8 in d ic a t e i f th e count i s t o ta k e p la ce

i n th e one, tw o, or f o u r 's p o s i t i o n . S im ila r ly , b i t s 9 t o 11 c o n ta in

th e req u ired in fo rm a tio n fo r th e Y co u n ter.

r "* * * C£) * 0

F i g . 1 . A AX

F i g . 1 . B A Y

e

<y &

r & o ( * *■ f- o 6 o

F i g . i . C R e p e a t

F i g u r e 1

INSTRUCTION WORD

B i t Number

0

1

2

6

7

B

10

11

... 1... T

1

0

1

1

0

...1...1"...

0

1

0

1

1

t

1

1

i

t

1

INT.

1

2

DATA WORD

B i t Number

0

1

2

_*

6

7

s

10

11

1

1

R

' r '"“

...

E

P

T

_ L ... 1....

... i... "" "T ..

S

A

X

... 1... ...i

s

r ..

r “

A Y

I .. 1...

KEPT

-

-

Number o f d o t s

S

; Count up

; Count down

A X ; a Y

-

No Count

•

- Count i n

' s p o s i t i o n

- Count i n

-' s p o s i t i o n

F i g u r e

I n s t r u c t i o n and Data Word C o n f i g u r a t i o n

B a s i c a l l y , th e d o t g en era to r c o n s is t s o f a c lo c k , down co u n ter,

(segm ent c o u n t e r ), decoding g a te s , an up/down counter and D/A

con-(6)

v e r t e r a s shown i n F igure 3» When a d o t i n s t r u c t i o n i s en cou n tered ,

a f l a g i s s e t up t o in d ic a t e t h a t th e d o t g en era to r i s t o b e i n i t i a t e d .

S h o r tly a f t e r th e f l a g i s s e t , a "load data" p u lse i s s e n t t o th e gen ­

e r a t o r . At t h i s tim e th e segment counter i s lo a d ed w ith th e number o f

d o t segm ents t h a t a re t o be g e n e ra ted . S im u lta n eo u sly w ith t h i s , th e

decoding c i r c u i t r y i s load ed w ith th e req u ired in fo rm a tio n t o in d ic a t e

i n what p o s i t i o n th e up/down c o u n ter s are t o be increm ented or decre­

m ented, When a l l th e d a ta has b een lo a d ed th e c lo c k i s i n i t i a t e d by

th e d ela y ed lo a d d a ta p u ls e , and th e p rod u ction o f th e d o ts i s begun.

The segment counter cou n ts u n t i l i t rea ch es z e r o , and a t t h a t tim e th e

c lo c k i s stopped and. a f l a g i s s e t t o in d ic a t e t h a t more d ata i s re ­

q u ire d , The p ro cess o f lo a d in g d ata and producing d o ts c o n tin u e s u n t i l

a new i n s t r u c t io n i s en cou n tered .

2 .2 Implement a t i on

The a c tu a l c i r c u i t was c o n str u c ted o f D i g i t a l Equipment Corpor-(3 )

a t i o n *R' s e r i e s m odules, u sin g n e g a tiv e HAM) l o g i c , i n which "0" v o l t s

r e p r e s e n ts a ‘f a l s e " and "-3" v o l t s r e p r e s e n ts a " tru e" . However, fo r

th e sake o f c l a r i t y , th e o p e r a tio n o f th e c i r c u i t w i l l be e x p la in e d ,

u sin g AND/OR l o g i c .

A diagram o f th e d o t g en era to r c i r c u i t u sin g AND/OR l o g i c i s

g iv e n i n F igure 4 . Whenever an in s t r u c t io n word i s decoded by t h e core

r e f r e s h c i r c u i t r y , a c le a r p u lse i s s e n t t o a l l th e g en era to r c o n tr o l

Rep ro duc ed w ith p er m is si o n of th e co p y rig h t owner . F u rt he r re pr od uc ti on p ro h ib ite d w ith o u t p e rm is si o n .

DBR

B i t s

6 t o 11

Dot

C ou nte r

D/S

C o n v e r te r

Horz.

Amo.

DBR

B i t s

Segment

Counter

Decoder

Dot

Mode

Dot

FF

O

J---C o n v e r t e r

V e r t

Dot

Counter

Load Data

To I n t e n s i t y

C i r c u i t

F i g u r e

X

,Y

Up

C

o

u

n

t

^

—

i—

,

I

To

Y

D

o

t

o j 3 H 3

C\J 3

O o o o o o

E-< O

O P P P P P P P

bD (1)

p cP

P 'r O (-H P O P O o CO o CO o CO

- B )h

CO

o

11

t o c le a r th e decoder b u ffe r r e g i s t e r (DR) so t h a t i t i s ready t o r e ­

c e iv e in fo rm a tio n i f th e d o t gen erator has been s e l e c t e d . I f i t i s a

d o t in s t r u c t io n Ijts a f t e r th e c le a r p u lse was s e n t , a 100 ns p u lse i s

se n t t o th e dot c o n tr o l f l i p f l o p (CFF) s e t t in g i t t o th e 1 s t a t e .

Approxim ately hOOns l a t e r a read d ata p u lse i s se n t t o th e d ot gener­

a to r which lo a d s th e r eq u ired in fo rm a tio n from th e d ata b u ffe r r e g i s t e r

(DBR) in t o th e segment cou nter (SC) and th e decoder b u ffe r r e g i s t e r (DR).

T his same p u lse a ls o s e t s th e data s ta t u s f l i p f l o p (SFF) t o in d ic a t e

t h a t no more d ata i s req u ired and s t a r t s th e c lo c k which i n i t i a t e s th e

segment co u n ter.

The c lo c k output i s g a ted t o th e decoder which s e l e c t s th e po­

s i t i o n i n which th e count i s t o tak e p la c e fo r both th e X and X d o t

c o u n te r s. The decoder a l s o in d ic a t e s th e d ir e c t io n i n which th e count

i s t o ta k e p la c e . The decoding i s done by u sin g a s e r i e s o f "AND” g a te s

fo r which o n ly one i n each o f th e X and X d ir e c t io n s has th e proper

in p u ts so as t o tu r n i t on.

A10 b i t up/down cou n ter and D/A co n v erter was a ls o needed f o r

th e g e n e r a tio n o f A/N ch a ra cters? however, i n order t o save d u p lic a tin g

the. c ir c u i t r y , p r o v is io n was made so t h a t th e d o t g en era to r co u ld use

th e same cou n ters and D/A c o n v e r te r s . Thus th e output o f th e decoder

i s s e n t t o th e ap p ro p ria te p o s it io n i n th e A/N up/down c o u n ter . I t

should be noted t h a t t h i s same counter has b een denoted as th e "dot

counter" when used i n r e fe r e n c e t o th e d o t g e n e ra to r. S im u lta n eo u sly

w ith th e sending o f th e p u lse t o th e d o t cou n ter, i n t e n s i t y p u ls e s are

s e n t t o th e i n t e n s i t y c i r c u i t which produce th e uriblanking p u ls e s

which a re required, t o g en era te d o ts on th e CRT. When th e segment counter

rea ch es z e r o , th e c lo c k i s d is a b le d and th e d ata s t a t u s f l i p - f l o p (SFF)

i s c le a r e d t o th e "0"s t a t e , in d ic a t in g t h a t e it h e r more d ata should be

s e n t t o th e d o t g e n e ra to r, or a new g en era to r should be i n i t i a t e d ,

2 .3 R e su lts and C onclusion s

An e q u iv a le n t o f th e above-m entioned c i r c u i t usin g "NAND" l o g i c

was implemented and connected t o th e r e fr e s h c o r e . T his c i r c u i t was t e s ­

t e d and performed a s e x p e c te d , A sample o f th e output from th e dot gen­

e r a to r i s g iv e n i n Figure 5* Figure %. i s a s e r i e s o f 3 sq u a r e s. Each

s id e o f th e o u tsid e square was c o n str u c te d by in crem en tin g or decrement­

in g th e counter a s r e q u ir e d , 15 s u c c e s s iv e tim es i n th e ^ ’ s count p o s i­

t i o n . S im ila r ly th e in n er sq uares were g en era ted u sin g 15 r e p e t i t i o n s

i n th e 2 ' s and l * s count p o s i t i o n . Figure 5B i s an approxim ate c i r c l e

which was drawn w ith th e d o t g e n e ra to r, in d ic a t in g th e f l e x i b i l i t y o f

th e d o t mode. There are a l s o some alphanum eric c h a r a c te r s on th e d ia ­

gram t o show t h a t both th e d o t and A/N g e n e ra to rs can use th e same

co u n ters and D/A c o n v e rter s w ith ou t any c o n f l i c t . Figu re 5C i n d i c a t e s

t h a t th e d o t g en era to r can a l s o produce l i n e s a t v a r io u s a n g le s . Thus

i t can be concluded t h a t th e d o t g en era to r has b een s u c c e s s f u l l y imp­

13

F i g . 5. A

A G r a c h i c a l D i s p l a y of I n c r e m e n t s i n t h e

,

c o u n t p o s i t i o n s

'!

F i g .

A G r a o h i c a l D i s o l a y of an a o p r o x l m a t i o n of a C i r c l e

F i g u r e 5

15

CHAPrER I I I

The I n t e n s i t y C ir c u it

3 .1 I n tr o d u c tio n

There are b a s i c a l l y two methods o f a c h ie v in g Z -a x is m odulation

on most d is p la y tu b e s . One method i s t o use p u lse width m odulation ,

which a llo w s th e b r ig h tn e s s o f th e d is p la y t o be v a r ie d by changing th e

w idth o f th e uhblanking p u ls e s w h ile th e p u lse am plitude i s h e ld c o n s ta n t.

'When u sin g t h i s method, th e i n t e n s i t y becomes b r ig h t e r as th e p u lse be­

comes w id er. The oth er method t h a t i s commonly used i s p u lse am plitude

m od ulation . The p u lse s i n t h i s c a se are a c o n sta n t width and th e in t e n ­

s i t y i s v a r ie d by in c r e a s in g or d e c re a sin g th e p u lse a m p litu d e. As th e

p u lse am plitude in c r e a s e s , th e i n t e n s i t y in c r e a s e s .

I n th e ca se o f th e d is p la y b ein g b u i l t a t th e U n iv e r s it y o f

Windsor, th e c h o ic e o f i n t e n s i f i c a t i o n methods a v a ila b le was lim it e d by

th e A /N g e n e ra to r. The g en era to r, accordin g t o d e s ig n s p e c i f i c a t i o n ,

was t o op erate a t a freq uen cy o f 2 m egacycles, which means t h a t th e rep ­

e t i t i o n p erio d i s 500 nanoseconds. However, due t o th e c h o ic e o f th e D /A

c o n v erter th a t was used i n th e A /N g e n e ra to r, 3 0 0 n a n o cy cles are re ­

q uired f o r th e D /A c o n v e r te r s t o s e t t l e t o t h e i r f i n a l v a lu e s . This a l ­

low s o n ly 200 nanoseconds fo r th e i n t e n s i f i c a t i o n t o ta k e p la c e , th u s

e f f e c t i v e l y e lim in a tin g th e p o s s i b i l i t y o f u sin g p u lse w idth modula­

t i o n , as t h i s i s not tim e enough t o g en era te 3 d i s t i n c t i n t e n s i t y l e v e l s .

3 . 2 I n t e n s i t y S e l e c t i o n

From th e s p e c i f i c a t i o n s g iv e n by Tektronex In co rp o ra ted , fo r th e

o s c il lo s c o p e b ein g used f o r th e d is p la y , i t was found t h a t n e g a tiv e p u ls e s (*0

betw een 3 and 50 v o l t s would b r ig h te n th e beam. I n order t o o b ta in

th r e e d i s t i n c t i n t e n s i t y l e v e l s f o r th e d is p la y , i t was r eq u ired t h a t th e

i n t e n s i t y c i r c u i t provide uriblanking p u lse s o f 3 d i f f e r e n t l e v e l s betw een

3 and 50 v o l t s . This was a ch iev ed by u sing a v o lta g e d iv id e r t o s e l e c t

th e req u ired uhblanking p u lse am p litud e. Uriblanking p u lse s are th en mod­

u la te d onto t h i s l e v e l , and r e s u lt in g p u lse s are a m p lifie d t o th e req u ired

v a lu e .

Figure 6 i s a diagram o f th e c i r c u i t used fo r i n t e n s i t y s e l e c t i o n .

A

t o supply power t o th e v o lta g e d iv id e r . However, th e f u l l i 5 v o l t s could

not be used b ecau se th e sw itc h e s used i n t h i s c i r c u i t were D i g i t a l Equip­

ment c o rp o ra tio n

"A"

sw itc h in g a maximum o f 10 v o l t s . Thus, a k.Y K dropping r e s i s t o r and a

zen er d iod e were used t o p rovide th e 10 v o l t supply needed t o f a c i l i t a t e

th e s w itc h e s . Two % p o ten tio m eters (P i and P2) were th e n connected i n

s e r i e s w ith th e 4.7K r e s i s t o r t o ground, t o com plete th e v o lta g e d iv id e r .

V arious p o t e n t ia ls betw een 0 and -1 0 v o l t s cou ld now be s e l e c t e d

from th e above m entioned c i r c u i t . The f u l l 10 v o l t s was connected t o one

s id e o f th e s in g le p ole s i r g l e throw e le c t r o n ic sw itch SIVI, th u s provid in g

th e p o t e n t ia l r eq u ired t o c r e a te maximum beam i n t e n s i f i c a t i o n . The cen tr e

ta p s o f p o ten tio m eters P i and P2 were connected t o one s id e o f sw itc h e s

SW2 and SW3 r e s p e c t i v e l y . These sw itch es provide fo r th e s e l e c t i o n o f

normal or dim i n t e n s i t i e s . The second s id e o f th e sw itc h e s are common

and p rovide th e output o f th e i n t e n s i t y s e l e c t i o n c i r c u i t .

The p o ten tio m eters add f l e x i b i l i t y t o th e system by a llo w in g

some c o n tr o l over th e beam b r ig h tn e s s when e it h e r th e normal or dim i n ­

t e n s i t i e s have b een s e l e c t e d .

A

Re produced w ith pe rm is si o n of the co p y rig h t owner . F u rt he r re pr od uc ti on p ro h ib ite d w ith o u t p e rm is si o n .

Large

.B r i g h t

SW

A/N

Dot

V e c t o r

S e l e c t

P u l s e s

Normal

IBR

swa

P2

^ 5 K b i t 1

Dim

sw6

Small

IBR

S o l i d

IBR

A/N Mode

A/N

C l e a r

b i t

&

A/N

-Dot

U n bl a n k i n g

P u l s e s

Das

IBR

PA

C l e a r

Dot! a t end o f v e c t o r

To Z

A x i s

L a s t P u l s e

From T.C.

PA

2

I n t . O ve r id e

F i g u r e 6

c i r c u i t r y can bo used by sim p ly a d ju s tin g th e p o ten tio m e te rs t o compen­

s a t e f o r th e d i f f e r e n t CRT phosphor.

The a c tu a l s e l e c t i o n o f i n t e n s i t y ta k e s p la c e i n th e fo llo w in g

manner. Each tim e an in s t r u c t i o n p u lse i s se n t t o any o f th e th r e e gen ­

e r a t o r s , b i t s 10 and 11 o f th e i n s t r u c t i o n word a re lo a d e d i n t o th e

I n t e n s i t y B u ffer R e g iste r (IBR) • The “AND" g a te s fo llo w in g th e IBR de­

code t h e s e two b i t s accord in g t o th e scheme shown i n T able 1 and c lo s e s

th e ap p ro p ria te sw itch (SWl, SW2, or SW3) s e l e c t i n g th e r eq u ired i n t e n ­

s i t y . I f a blanked i n t e n s i t y i s chosen , none o f th e sw itc h e s are c lo s e d ,

th u s y ie ld in g a zero l e v e l output from th e s w itc h e s .

At t h i s p o in t i n th e c i r c u i t , com pensation i s in tro d u ced fo r

th e in c o n s is t e n c ie s i n th e A/N g e n e r a to r . The output o f th e

above-mentioned v o lta g e d iv id e r d oes n ot go d i r e c t l y t o th e p u ls e a m p lifie r ;

in s t e a d , i t becomes th e in p u t t o a second v o lta g e d iv id e r t h a t c a r r ie s

out th e com pensation f o r th e A/N g e n e r a to r . Sw itch es SWf, SW5 and SW6

i n t h i s c a se a re c o n t r o lle d by th e A/N g en era to r when i t i s i n u s e .

I f a la r g e l e t t e r i s b ein g drawn on th e CRT, SW^ i s c lo s e d , ap p lyin g th e

f u l l output p o t e n t ia l from th e i n t e n s i t y s e l e c t i o n c i r c u i t t o th e p u lse

a m p lif ie r . T his ca u ses th e d o ts composing th e l e t t e r t o be b r ig h te r

th a n normal, th u s com pensating f o r th e f a c t t h a t th e d o ts a re spread

fa r th e r ap art th a n norm al. When normal s i z e c h a r a cter s a re b ein g drawn,

SW5 i s c lo s e d app lyin g th e normal i n t e n s i t y p o t e n t ia l t o th e p u lse amp­

l i f i e r . T his p o t e n t ia l i s s l i g h t l y low er th a n t h a t used when la r g e l e t ­

t e r s a re b ein g drawn, a s th e r e i s a v o lta g e drop a c r o ss th e p o ten tio m eter

P3» When sm all l e t t e r s are drawn, SW6 i s c lo s e d , th u s cau sin g a smal­

19

I n t e n s i t y B i t s

B i t s

and

I n t e n s i t y

00

Normal

01

Dim

10

B r i g h t

11

Blanked

V e c t o r S e l e c t i o n B i t s

and

8

B i t s

and g

V e c t o r Type

01

Dot a t Tip of V e c t o r

10

Dash L i n e

11

S o l i d L i n e

T a b le

I d e n t i f i c a t i o n of B i t P o s i t i o n s

P r o v isio n was a ls o made so th a t th e normal sw itc h SW5 i s c lo s e d

when any g en era to r o th er th a n th e A/N g en era to r i s i n u s e . The A/N s t a t u s

f l i p f l o p (A/N FF) was used t o a c h ie v e t h i s end. Whenever th e A/N gen­

e r a to r i s i n use t h i s f l i p f l o p i s s e t t o th e "1" s t a t e , th u s g iv in g th e

A/N g en era to r c o n tr o l o f th e com pensation network. However, when th e A/N

g en era to r i s n ot i n u se , th e A/N f l i p f l o p i s c le a r e d t o th e "O'’ s t a t e ,

th u s e f f e c t i v e l y b lo c k in g th e s ig n a ls from th e A/N g e n e r a to r . Sw itch SW5

i s a l s o fo r c e d t o c lo s e and sw itc h e s SW^ and SW6 are fo r c e d t o open i f

th e y were c lo se d p r e v io u s ly . I n th e c a se o f th e A/N and d o t g e n e r a to r s ,

t h e unblanking p u ls e s from th e g e n e r a to r s a re s e n t d i r e c t l y t o th e p u lse

a m p lifie r (PA 1 ) , where th e y a re modulated w ith th e s e le c t e d i n t e n s i t y

l e v e l , th u s c r e a tin g th e r eq u ir ed unbl&nking p u ls e s . A fu r th e r d e s c r ip ­

t i o n o f th e p u lse a m p lifie r w i l l be g iv e n i n th e n ext s e c t io n o f t h i s

c h a p ter .

I t should be noted t h a t a d d it io n a l in fo rm a tio n i s r eq u ir ed by

th e i n t e n s i t y c i r c u i t when a v e c to r i s being drawn. Thus, whenever a

VECTOR i n s t r u c t i o n i s g iv e n , b i t s 7 and 8 o f t h e i n s t r u c t io n word are

a ls o lo a d ed in t o th e IBR. These b i t s c o n ta in in fo rm a tio n p e r ta in in g t o

th e ty p e o f v e c to r t o be drawn. The coding o f t h e s e two b i t s i s g iv e n

i n Table 1 .

The o p e r a tio n o f th e v e c to r p u lse a m p lifie r (PA 2 ) i s s l i g h t l y

d i f f e r e n t from th e o p e r a tio n o f th e DOT, A/H p u lse a m p lif ie r . The out­

21

e l e c t r o n i c sw itch (SW?)• The o th er s id e o f th e sw itch i s con nected t o

th e in p u t o f th e v e c t o r p u lse a m p lifie r # T his sw itch i s operated by

t r ig g e r p u ls e s from v a r io u s p o in ts i n th e v e c t o r c i r c u i t r y , depending

on what ty p e o f v e c to r i s b ein g drawn. These p u ls e s a re th e n a m p lifie d

t o th e r eq u ired l e v e l by th e v e c to r p u lse a m p lif ie r .

The most commonly used v e c t o r i s th e s o l i d lin e # I n t e n s i f i ­

c a t io n o f t h i s ty p e o f v e c to r i s a ch iev ed by c lo s in g SW? and h o ld in g i t

c lo s e d f o r th e f u l l le n g th o f tim e t h a t th e v e c to r i s b e in g g e n e ra ted .

T h is c r e a t e s one uhblanking p u lse which b r ig h te n s th e beam throughout

th e f u l l d isp lacem en t o f th e beam, th u s c r e a tin g a s t r a ig h t l i n e . A s e c ­

ond ty p e o f v e c t o r i s th e dashed l i n e # I n t e n s i t y p u ls e s f o r t h i s ty p e

o f v e c to r are produced by u sin g th e output o f b i t 1 o f th e "tim er counter"

t o o p era te th e s w itc h . A more d e ta ile d , d e s c r ip t io n o f th e "tim er counter"

w i l l be g iv e n i n th e n ex t c h a p ter . By u sin g th e output o f th e counter

a s t r ig g e r p u ls e s , t h e sw itch i s r e p e a te d ly c lo s e d f o r a p erio d o f tim e ,

and th e n opened f o r th e same p erio d o f tim e , th u s c r e a tin g a dashed l i n e ,

a s th e p u lse a m p lifie r i s c o n t in u a lly b ein g tu rn ed on and o f f . The l a s t

ty p e o f v e c to r i s a blanked v e c to r t h a t has a d o t a t th e end o f i t t o

in d ic a t e where th e v e c t o r ended. I n t e n s i f i c a t i o n o f t h i s ty p e o f v e c to r

i s a ch iev ed by blan kin g th e Z -a x is u n t i l th e v e c to r i s com p lete, and th e n

one i n t e n s i t y p u lse i s se n t t o th e Z -a x is , c r e a tin g one d o t a t th e end

o f th e v e c t o r . The l a s t p u lse from th e "tim er counter" i s used t o e r e a te

t h i s uhblanking p u lse by m om entarily c lo s in g sw itch 7 ,

One fu r th e r fe a tu r e o f th e i n t e n s i t y c i r c u i t rem ains t o be men­

t io n e d . T his i s th e i n t e n s i t y o v e r r id e fe a tu r e which i s a v a ila b le o n ly

been s p e c i f i e d by th e i n t e n s i t y c i r c u i t . B it 1 o f th e second d ata word

fo r th e v e cto r g en era to r c o n tr o ls th e use o f t h i s o p tio n . I f t h i s b i t

i s a 1 , th e output o f th e i n t e n s i t y s e l e c t i o n c i r c u i t i s o v errid en , and

a blanked v e c to r i s drawn. T h is o p tio n was in co rp o ra ted fo r th e conven­

ie n c e o f th e programmer, as i t a llo w s one t o sw itch from blanked t o un­

blanked i n t e n s i t i e s w ith o u t g iv in g a new in s t r u c t io n each tim e t h i s i s

don e. An added advantage l i e s i n th e f a c t t h a t t h i s fe a tu r e a ls o sa v es

core space a s e x tr a i n s t r u c t io n words are not req u ired f o r changing i n ­

t e n s i t i e s .

3 .3 Pu lse A m p lifie r s

( i ) Dot and A/N P u lse A m p lifier

A sch em atic diagram o f th e p u lse a m p lifie r t h a t was d esig n ed fo r

th e DOT and A/N g e n e ra to rs i s g iv e n i n Figure 7 . T r a n sis to r s and Q£

and t h e i r a s s o c ia te d e m itte r r e s i s t o r each form e m itte r f o llo w e r s which

were b u i l t t o preven t lo a d in g o f th e i n t e n s i t y s e l e c t i o n c i r c u i t , and th e

t r ig g e r c i r c u i t s , r e s p e c t i v e l y . Once th e d e s ir e d i n t e n s i t y l e v e l has

b een s e le c t e d by th e i n t e n s i t y c o n tr o l c i r c u i t , a corresponding D. C.

v o lta g e i s a p p lie d t o th e b a se o f t r a n s is t o r Q^. S in ce t h i s t r a n s is t o r

i s i n th e e m itte r fo llo w e r c o n fig u r a tio n , t h i s D. C. v o lta g e i s trans­

m itte d t o th e e m itte r o f t r a n s is t o r Q^» and a l s o t o th e b ase o f t h i s

t r a n s i s t o r through th e 3»9 K r e s i s t o r . S in ce th e b a se and e m itte r o f

t h i s t r a n s is t o r are a t app roxim ately th e same p o t e n t i a l , t h i s t r a n s i s ­

Re produced w ith pe rm is si o n of the co p y rig h t owner . F u rt he r re pr od uc ti on p ro h ib ite d w ith o u t p e rm is si o n .

- 15V - 55V

INPUT

LEVEL

, 1 0 0 /-' h I—

e~ej2Ji

l b O of

C l

o . o o i ^ r

UNBLANKING PULSES

1

OUTPUT

COMPONENT

NUMBER

0,1, 0 , 2 , 0 /

Q5»Q6

Q3

D

D

D3

2

N

N

RA

2N3261

1N3754

1N914 1R5A4

D

F i g u r e 7

D o t a n d A /N P u l s e A m p l i f i e r

c i r c u i t t o p rovid e i s o l a t i o n betw een th e e m itte r fo llo w e r (Q^) and th e

t r a n s i s t o r sw itch (Q^)»

T rig g er p u ls e s which a re c r e a te d by th e a p p ro p ria te g en era to r

a re a p p lie d t o th e b ase o f t r a n s i s t o r Q2 and a re tr a n sm itte d t o th e b ase

o f t r a n s i s t o r Q3 through th e co u p lin g c a p a c ito r C^» These t r ig g e r p u ls e s

a re p o s i t i v e go in g p u ls e s which tu r n t r a n s is t o r Q-j'fen", cau sin g i t t o

con d u ct. T h is ca u ses a p u lse t o be a p p lie d t o th e b a se o f t r a n s i s t o r Q^,

which i n c o n ju n c tio n w ith t r a n s i s t o r Q^, makes up a p u lse a m p lif ie r .

T r a n sisto r Q5 and i t s a s s o c ia t e d e m itte r r e s i s t o r c o n s t it u t e another em it­

t e r fo llo w e r which p ro v id es i s o l a t i o n betw een th e p u lse a m p lifie r and th e

Z -a x is o f th e o s c i l l o s c o p e . The e m itte r o f t r a n s i s t o r i s connected

t o d io d e D2, shown i n Figure 8 , which i s one h a l f o f a d iod e "OR" g a t e ,

which i n tu rn i s connected t o th e Z -a x is o f th e o s c i l l o s c o p e .

( i i ) V ector P u lse A m p lifie r

The p u lse a m p lifie r used by th e v e c to r g en era to r i s s l i g h t l y

l e s s com plicated th an th e d o t and A/N p u lse a m p lif ie r . The r ea so n fo r

t h i s l i e s i n th e f a c t t h a t th e i n t e n s i t y l e v e l and uhblanking p u ls e s a re

modulated i n th e i n t e n s i t y s e l e c t i o n c i r c u i t r y , so t h a t th e p u lse am pli­

f i e r m erely a m p lif ie s t h e p u ls e s t o th e req u ired p o t e n t i a l s . Figure 8 i s

a schem atic diagram o f th e p u lse a m p lifie r used by th e v e c to r g e n e r a to r .

T r a n sis to r s Qj. and Q2 and t h e i r a s s o c ia t e d c i r c u i t r y com prise th e a c tu a l

a m p lif ie r . T r a n sisto r Q3 and i t s a s s o c ia t e d e m itte r r e s i s t o r a re c o n ­

n ected i n th e e m itte r fo llo w e r c o n fig u r a tio n t o p rovid e i s o l a t i o n betw een

t h e p u lse a m p lifie r and th e Z - a x is . Diode D 1 i s th e second h a l f o f th e

25

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V

e

c

to

r

p

u

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e

A

m

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ie

so t h a t th e y can be connected t o th e Z -a x is .

3 .4 R e su lts and C onclusions

The above m entioned p u lse a m p lif ie r s were c o n str u c ted and mounted

on D i g i t a l Equipment C orporation "blank modules" t o f a c i l i t a t e rack mount­

i n g . An e q u iv a le n t o f th e diagram shown i n F igure 6 was c o n str u c te d usin g

"HAND''logic, and t h i s c i r c u i t alon g w ith th e p u lse a m p lifie r s was con­

n ected t o th e computer te r m in a l t h a t was b ein g b u i l t .

The i n t e n s i t y s e l e c t i o n c i r c u i t r y was t e s t e d and found t o op erate

p r o p e r ly . That i s , when in s t r u c t io n s were g iv e n t o s e l e c t NORMAL, DIM,

BRIGHT or BLANKED i n t e n s i t i e s , th e ap p ro p ria te c i r c u i t r y was i n i t i a t e d .

A ls o , when th e A/N g en era to r was b ein g used, th e compensating c i r c u i t s

were s e le c t e d a s ex p e cted , However, i t was found t h a t when 50 v o l t un­

b lan k in g p u ls e s were used, th e d is p la y tended t o d e fo c u s, making th e

d is p la y b lu r r y . A c le a r d is p la y was ob tained by reducing th e i n t e n s i t y

p u ls e s t o 30 v o l t s . However, t h i s r e d u c tio n e lim in a te d th e p o s s i b i l i t y

o f having th r e e d i s t i n c t i n t e n s i t y l e v e l s fo r th e p resen t tim e , s in c e

approxim ately 20 v o l t s was req u ired t o i n t e n s i f y th e beam w ith such a

sh o rt p u ls e . T his meant t h a t th e r e was o n ly a 10 v o l t change between

th e dim and b r ig h t i n t e n s i t y l e v e l s , and t h i s was not enough t o c r e a te

th r e e d i s t i n c t b r ig h tn e ss l e v e l s . S in ce th e s e l e c t i o n c i r c u i t o p e r a te s

as expected, only a few changes w i l l have t o be made t o obtain th e three

l e v e l i n t e n s i f i c a t i o n when a d is p la y tube on which th e a stig m a tism may

be a d ju ste d , i s o b ta in e d .

S o lid l i n e s , dashed l i n e s and blanked l i n e s w ith a d o t a t th e to p

27

i n t e n s i f i c a t i o n c i r c u i t s are o p era tin g p r o p e r ly . The i n t e n s i t y o v e rr id e

c i r c u i t was a ls o t e s t e d and found t o op erate a s e x p e cted . Whenever b i t 1

o f th e Y co o rd in a te data word was a 1, a blanked v e c to r was drawn, no mat­

t e r what i n t e n s i t y had been chosen by th e i n t e n s i t y s e l e c t i o n c i r c u i t r y ;

and whenever t h a t b i t was a 0 , th e i n t e n s i t y s e l e c t i o n c i r c u i t had con­

t r o l o f th e b r ig h t n e s s . Thus i t i s concluded t h a t th e i n t e n s i t y c i r c u i t s

were s u c c e s s f u lly c o n str u c te d .

CHAPTER IV

The V ector Generator

^ .1 In tr o d u c tio n

There a re b a s i c a l l y two methods commonly used t o g e n e ra te a

v e c t o r . One method u se s p r im a r ily d i g i t a l c i r c u i t r y , w h ile th e oth er

u se s p rim a r ily analog c i r c u i t r y . The d i g i t a l method produces v e c to r s

p r in c ip le t h a t i f a f ix e d tim e i s a llo w ed t o g e n e ra te a v e c t o r , th e

r a t i o o f th e beam v e l o c i t y i n th e Y d i r e c t i o n t o th e beam v e l o c i t y i n

th e X d ir e c t io n i s th e s lo p e o f th e l i n e . A sim p le 4- s ta g e b in a r y r a te

m u lt ip l ie r i s shown i n Figure 9» The o p e r a tio n o f t h i s c i r c u i t can b e s t

be e x p la in ed by u se o f an example which i n t h i s c a se w i l l be a l i n e w ith

s lo p e 5/ 8 .

I n order t o draw a v e c t o r , a s e r i e s o f p u ls e s must be s e n t t o th e

p o s i t i o n co u n ters which cau se th e beam t o be d is p la c e d . The in p u t p u lse

t r a i n i s se n t d i r e c t l y t o th e X p o s i t i o n counter and a l s o t o th e BRM,

which produces th e p u lse s t h a t a re s e n t t o th e Y p o s i t i o n c o u n te r . S in ce

t h i s l i n e i s t o have a s lo p e o f 5/ 8 , th e b in a ry e q u iv a le n t o f t h i s slo p e

which i s 1010, i s load ed i n t o th e p ro p o rtio n s e l e c t o r . T h is i n tu r n e n ­

a b le s th e "AND" g a te s which a re conn ected t o th e "0" s id e o f th e BRM f l i p

f l o p i and f l i p f l o p 3» Thus a s th e in p u t p u lse s increm ent th e BRM coun­

t e r , th e "0" t o "1" t r a n s i t i o n s o f FFl and FF3 a re tr a n sm itte d v ia th e AND

g a te and combining "OR" g a te t o th e Y p o s it io n c o u n te r . S in ce o n ly two

o f th e AND g a te s a s s o c ia t e d w ith th e BRM are enabled by th e p ro p o rtio n

s e l e c t o r f o r e v ery 16 in p u t p r i s e s , o n ly 10 p u ls e s are ou tput b y th e BRM.

Thus a l i n e w ith slo p e 5 /8 i s gen era ted as shown i n Figure 10.

Re produced w ith pe rm is si o n of the co p y rig h t owner . F u rt h er re pr od uc ti on p ro h ib ite d w ith o u t p e rm is si o n .

P r o p o r t i o n

S e l e c t o r

I n p u t

P u l s e

Tr ain

To V e r t .

_

d/a

C o n v e r t e r

P o s i t i o n

Counter

BRM

F F k

FF3

FF1 FF2

To Horz

D/A

Amp

P o s i t i o n

C ou nte r

C o n v e r t e r

F i g u r e

B i n a r y Rate M u l t i p l i e r

P

u

ls

e

s

\

31

A c lo s e exam ination o f Figure 10 r e v e a ls t h a t th e Bill'd g e n e r a te s

a s t a ir c a s e t h a t o n ly approxim ates th e i d e a l s t r a ig h t l i n e 1, ©cod herein l i e s

one o f th e in h e r e n t f a u l t s w ith t h i s method o f v e c to r g e n e r a tio n . A se c ­

ond problem i s th e erro r in tro d u ced when th e s lo p e o f th e l i n e i s conver­

t e d in t o a f r a c t i o n a l b in a ry number i n order t o be com patible w ith th e

p ro p o rtio n s e l e c t o r . The r e s o lu t io n o f th e slo p e v a lu e which i s a p p lie d

t o th e p ro p o rtio n s e le c t o r c i r c u i t r y depends on th e BRM counter s i z e ,

s in c e each b i t o f th e s lo p e v a lu e i s a s s o c ia te d w ith one sta g e o f th e

c o u n te r . However, i n most c a s e s , t h i s i s not to o s e r io u s a problem, f o r

i f a 10 b i t r e g i s t e r i s used , i t r e p r e s e n ts an e rro r o f .1 $ . One o th er

problem th a t a r i s e s i n t h i s ty p e o f v e c t o r g en era to r i s th e f a c t t h a t i t

te n d s t o be slow , s in c e a s e r i e s o f co u n ters are used t o g e n e ra te th e

v e c t o r . The slo w n ess o f th e BRM i s i t s most im portant f a u l t .

Because o f th e above mentioned rea so n s , i t was d ecid ed t o use

analog te c h n iq u e s ra th e r th a n d i g i t a l . However, a c e r t a in amount o f

d i g i t a l c i r c u i t r y was req u ir ed s in c e th e d a ta output from th e co re i s i n

d i g i t a l form. T h is d ata must be changed t o analog form and t h i s i s per­

formed by using th e D/A c o n v e r te r s mentioned i n Chapter I I . Due t o th e

f a c t t h a t 10 b i t r e g i s t e r s were used i n c o n ju n c tio n w ith th e D/A con­

v e r t e r s , 2 d ata words were req u ired by th e v e c to r g e n e r a to r . The f i r s t

da ta word i s th e X c o o rd in a te word and c o n ta in s th e in fo rm a tio n req u ired

by th e X d e f l e c t i o n c i r c u i t r y , w h ile th e second word c o n ta in s th e in f o r ­

m ation req u ired by th e I d e f l e c t i o n c i r c u i t r y . Each word c o n ta in s th e

c o o rd in a te o f th e end p o in t o f th e v e c to r r e l a t i v e t o th e o r ig in which i s

lo c a t e d a t th e low er l e f t hand s id e o f th e CRT. These c o o r d in a te s a re

changed from a b s o lu te t o r e l a t i v e c o o r d in a te s by th e analog c i r c u i t s .