The design of a buffer for communication between tape drive and digital computer

The design of a buffer for communication between tape drive and digital computer

Item Type text; Thesis-Reproduction (electronic) Authors Daniel, Wilton Jeston, 1940-

Publisher The University of Arizona.

Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona.

Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.

Download date 09/09/2021 05:00:09

Link to Item http://hdl.handle.net/10150/319798

THE DESIGN OF A BUFFER FOR,COMMUNICATION BETWEEN TAPE DRIVE AND DIGITAL COMPUTER

b y

W ilto n J e D a n ie lj J r „

'i -

A T h e s is S u b m itted t o th e F a c u lty o f th e DEPARTMENT OF ELECTRICAL ENGINEERING I n P a r t i a l F u l f i l l m e n t o f th e R equirem ents

F o r th e D egree o f MASTER OF SCIENCE In th e G rad u ate C o lle g e The U n iv e r s ity o f A riz o n a

1 9 6 h

STATEMENT BY AUTHOR

T h is t h e s i s has b een s u b m itte d i n p a r t i a l f u l f i l l m e n t o f re q u ire m e n ts f o r an advanced d e c re e a t th e U n iv e r s ity o f A riz o n a and i s d e p o s ite d i n th e U n iv e r s ity L ib r a r y t o be made a v a i l a b l e t o b o rro w e rs u n d e r r u l e s o f th e L i b r a r y .

B r i e f q u o ta tio n s from t h i s t h e s i s a r e a llo w a b le w ith o u t s p e c i a l p e rm is s io n , p ro v id e d t h a t a c c u r a te acknow ledgm ent o f s o u rc e i s made. R e q u e sts f o r p e rm is s io n f o r e x te n d e d q u o ta t io n from o r re p r o d u c tio n o f t h i s m a n u s c rip t i n w hole o r i n p a r t may be g ra n te d b y th e head o f th e m ajo r d e p a rtm e n t o r th e Dean o f th e G rad u ate C o lleg e when i n h is judgm ent th e p ro p o sed u se o f th e m a t e r i a l i s in th e i n t e r e s t s o f s c h o l a r s h i p . In a l l o th e r i n s t a n c e s , how ever, p e rm is s io n m ust be o b ta in e d from th e a u th o r .

APPROVAL BY THESIS DIRECTOR

T h is t h e s i s has b e en approved on th e d a te shown b e lo w :

GERALD R. PETERSON

A s s o c ia te P r o f e s s o r o f E l e c t r i c a l E n g in e e rin g

AC KNOWLEDCMENT

The a u th o r w is h e s t o e x p r e s s h i s a p p r e c i a t i o n t o D r⁰ G e rald R«, P e te r s o n f o r h i s encouragem ent and many h e l p f u l s u g g e s tio n s d u r­

in g th e work on t h i s t h e s i s⁰ I w ould a l s o l i k e t o th a n k M ich ael L a r r iv a f o r th e tim e he s p e n t d is c u s s in g th e problem s t h a t a ro s e i n th e b u f f e r d e sig n ,, W ith o u t th e h e lp o f th e s e two p e o p le p t h i s t h e s i s w ould n o t have b een completed®

i i i

TABLE OF CONTENTS

LIST OF ILLUSTRATIONS 0 s «

ABSTRACT o e o o o o o o o o o o o o e e e

CHAPTER 1 INTRODUCTION , .

101 D i g i t a l Computer

102 Tape ^tirlVe e e e o o e o o

CHAPTER 2 SYSTEM REQUIREMENTS „

2 01 Computer o o o o o e o o o 2 02 Tape D riv e » c e « »

2 03 Sequence o f O p e ra tio n s e o

CHAPTER 3 LOGIC DESIGN , .

3 o l F u n ctio n C o n tro l C i r c u its 3 .2 Tape C o n tr o l C i r c u i t s ® « 3 .3 W rite C i r c u i t s • ,

3,U Read C i r c u i t s 3 .5 C ost E s tim a te „ 3 .6 C onclusion

e e o o o o o o o

o o o o o o o o o

O C 0 0 O O O O O

O 0 O O O O O O O O O O O

o o o o o o o o o

o o o o o o o o o o o o o o

o o o o o o o o o

O O O O O O O O O O O D

o o o o o o o o o

o o o o o o o o o

o o o o o o o o o

o o o o o o o o o

o o o o o e o o o o o o o

O O O O O O D O O O O O O O O

o o o o o o o o o o o o o o

o o o o o o o o o o o o o o o

APPENDIX ^{0 0 6 o 0 6 O © 0 6 O O O O O O O ©}

A yl O u tp u t Program

A .2 I n p u t Program . . . . A .3 Tape Form at

0 0 0 0 0 0 0 0 0 0 0 0 0 0 6

o o o o o o o o o

REFERENCES o o o o ©

o o o o o o o o o o o o o o o o

o o o o o o o o o o o o o o o o o < ^

Page

V

v i i 1

1

8 10

10 11 12

17 17 20

25 36 U6

h7

U8

U8

U9 51 53

i v

LIST OF ILLUSTRATIONS

Page F ig u re

1 .1 COMPUTER WORD o o o o o o a o o o o o o o o o o o e e 2

1 02 COMPUTER CONTROL BLOCK DIAGRAM 5

1 . 3 COMPUTER DATA FLOW . . . . . . . . . . . 6

l . i t TAPE DATA FXXDW . . . . . . P 3 .1 BUFFER UNIT BLOCK DIAGRAM . . . 18

3 .2 LOGIC SYMBOLS . . . o IP 3 .3 SELECT DECODE CIRCUIT . . . 21

3.1* OPERATION DECODE CIRCUIT . . . 21

3 .5 TAPE CONTROL CIRCUITS . . . 23

3 .6 READ SPROCKET . . . o 21* 3 .7 WRITE CIRCUIT BLOCK DIAGRAM . . . 2?

3 .8 DISASSEMBLY CIRCUITS . . . 28

3 .P MODULO 5 COUNTER . . . o . . . 2p 3 .1 0 PARITY GENERATE CIRCUITS . . . 31

3 .1 1 WRITE PARITY CHECK CIRCUITS . . . 32

3.12 WRITE TAPE MOTION CIRCUITS . . . 33

3 .1 3 WRITE TIMING SEQUENCE CIRCUIT . . . 31*

3.11* READ CIRCUIT BLOCK DIAGRAM . . . 37

3 .1 5 ASSEMBLY CIRCUITS . . . 38

3 .1 6 READ PARITY CHECK CIRCUITS . . . 1*0

3 .1 7 LONGITUDINAL CHECK CIRCUITS . . . 1*2

LIST OF ILLUSTRATIONS—C ontinued

Page F ig u re

3018 READ TAPE MOTION CIRCUITS o o o o . o c o o o o o o o lt3

3019 READ TIMING SEQUENCE CIRCUIT 0 = o o o . c » o e » o k h

A ol OUTPUT PROGRAM o o o o o o o o e o o o o o o o o o o

A©2 INPUT PROGRAM o o o o o o o o s o e o o o o o o o o o 50

A o 3 TAPE FORMAT © o o e o o o e e e e o o o o o o o o o o 52

ABSTRACT

T h is t h e s i s p r e s e n t s a d e s ig n o f a b u f f e r u n i t w h ich c o n t r o l s com m unication betw een an e x p e rim e n ta l G e n e ra l E l e c t r i c d i g i t a l com­

p u t e r and a m a g n etic ta p e d r iv e m a n u fa ctu red by I n t e r n a t i o n a l B u sin e ss M achin es0

F i r s t a g e n e r a l d is c u s s i o n o f th e two u n i t s in v o lv e d i s p r e ­ sented® Then, th e t h e o r e t i c a l re q u ire m e n ts t o a llo w th e d i g i t a l com puter t o c o n t r o l th e ta p e d r iv e i s discu ssed ®

A d e s ig n o f a b u f f e r u n i t t o m eet th e above re q u ire m e n ts i s ex plained® T h is d e s ig n i s b a se d on two b a s i c s p e c if ic a tio n s ® F i r s t , th e m a j o r i t y o f c o n t r o l o f th e ta p e d r iv e i s p erfo rm ed in d e p e n d e n tly o f th e d i g i t a l com puter t o a llo w th e maximum amount o f i n t e r n a l mem­

o ry t o be u sed f o r o th e r p u r p o s e s « S e c o n d ly , w henever a c h o ic e i n d e s ig n re q u ire m e n ts i s a v a i l a b l e , th e more g e n e r a l m ethod i s u sed t o a llo w maximum f l e x i b i l i t y ®

v i i

CHAPTER 1 INTRODUCTION

The v a r i e t y o f jo b s f o r w hich th e m odern, g e n e r a l p u rp o se , d i g i t a l com puter i s u sed r e q u i r e s t h a t th e s e co m p u ters be a s f l e x i b l e a s p o s s i b l e w h ile re m a in in g e c o n o m ic a l. The f l e x i b i l i t y o f an y g iv e n m achine i s d e te rm in e d l a r g e l y b y th e s i z e o f memory i n t h a t m ach in e.

The m achine w ith a s m a ll memory w i l l b e l e s s v e r s a t i l e th a n th e

m achine w ith a la r g e memory. The d i g i t a l com puter w ith w hich t h i s r e ­ p o r t i s c o n ce rn e d h as an i n t e r n a l c a p a c i t y o f o n ly $ 1 2 w o rd s. S in c e an IBM Tape D riv e Model 727 i s a v a i l a b l e , i t was d e c id e d t o u se t h i s u n i t t o in c r e a s e th e memory i n th e d i g i t a l co m p u te r. T h is t h e s i s d e s c r ib e s th e d e s ig n o f a b u f f e r u n i t t o a llo w th e com puter t o com­

m u n icate w ith th e ta p e d r iv e *

1 ,1 D i g i t a l Computer

The d i g i t a l co m p u te r, w hich i s th e c e n t e r o f th e s y s te m , i s a s o l i d s t a t e , e l e c t r o n i c com puter u t i l i z i n g d io d e and t r a n s i s t o r l o g i c . The com puter u s e s asy n ch ro n o u s l o g i c w hich a llo w s e ac h e l e c ­ t r o n i c c i r c u i t to o p e ra te a t i t s own c h a r a c t e r i s t i c s p e e d . C om pletion s i g n a l s a r e g e n e r a te d w i t h i n e ac h l o g i c a l b lo c k t o a llo w th e o p e r a tio n s t o s h i f t t o a n o th e r c o n t r o l b lo c k . The sp eed o f th e com puter i s com­

p a r a b le t o sy n ch ro n o u s m achines o f t e n m egacycle c lo c k fre q u e n c y .

The com puter w ord c o n s i s t s o f e i g h t o c t a l c h a r a c t e r s p lu s s ig n ( F i g , 1 , 1 ) , Each o c t a l c h a r a c t e r i s form ed b y t h r e e b i n a r y b i t s , and

26 24 26 22 21 20 19 Id 17 16 15 14 16 12 II 10 9 & 7 (o 5 4 5 2 1

26 15 14 15 12 II 10 9 8 7 la 6 4 5 2 1

O p C o d e 4 f c i t e

I n f o r m a t i o n

I n s t r J c t i o n s

A d d ret,t>

JO

FIGURE 1 .1 COMPUTER WORD

th e s ig n c o n s is ts o f one b in a ry b it* N um erical d a ta a re handled i n a b in a r y coded r e p r e s e n t a t i o n » For p o s it i v e numbers th e norm al b in a r y

coded r e p r e s e n ta tio n i s u sed : f o r n e g a tiv e numbers th e tw o 's comple­

ment form i s used* The s ig n o f th e number i s in d ic a te d by b i t 25>j 0 i f p o s i t i v e s 1 i f n e g a tiv e *

I n s t r u c t i o n words a re i n a s in g le a d d ress form at* In an i n ­ s t r u c t i o n , on ly b i t s l- ll* , 15 and 25 a re used* B its 1 -1 0 c o n s titu te th e ad d re ss f i e l d , w h ile b i t s 11-H i d e s ig n a te th e o p e ra tio n code*

S p e c ia l o p e ra tio n s may be perform ed by i n s e r t i n g b i t s i n p o s itio n s 15 and 25* I f b i t 25 i s a " one" i n an i n s t r u c t i o n , i n d i r e c t a d d re ss in g occurs* T hat i s , th e a d d re ss s p e c if ie d by th e i n s t r u c t i o n r e p re s e n ts th e a d d re ss i n memory w hich c o n ta in s th e ad d re ss o f th e d a ta upon which th e i n s t r u c t i o n i s to o p erate* T his a llo w s th e computer to t r e a t th e a d d ress o f th e in fo rm a tio n as data* When b i t 15 i s one, th e computer w i l l i n t e r r u p t i t s program t o allo w d a ta t o be tra n s m itte d through

th e p e r ip h e r a l i n t e r f a c e a d a p te r , which c o n s is ts of two 8 b i t b u f fe r s and a 7 b i t b u ffe r* This i n t e r r u p t f e a tu r e e n a b le s th e computer to o p e ra te a t i t s te n m egacycle r a t e w ith o u t e x c e ssiv e tim e used f o r i n ­ p u t-o u tp u t*

The com puter i s o rg a n is e d i n t o ^{1 6} l o g i c a l c o n t r o l b lo c k s * W ith in e ac h c o n t r o l b lo c k s e v e r a l o p e r a tio n s a re p e rfo rm e d s im u lta n ­ e o u s ly and in d e p e n d e n tly o f one a n o th e r* As each o p e r a tio n i s com­

p l e t e d , a s i g n a l i s g e n e ra te d * Only when a l l th e c o m p le tio n s i g n a l s f o r e a c h o p e r a tio n i n t h a t b lo c k have b e en r e c e iv e d w i l l th e m achine s h i f t i n t o th e n e x t c o n t r o l blo ck *

F ig u re 1 .2 r e p r e s e n t s th e o r g a n iz a ti o n o f th e 16 c o n t r o l b lo c k s „ B lo ck s 1-U and 1$ c o n s t i t u t e th e a n a l y s i s , o r f e t c h c y c l e , I n th e a n a l y s i s c y c le th e i n s t r u c t i o n i s b ro u g h t from memory, b ro k e n down i n t o i t s s e p a r a t e p a r t s , and s to r e d i n th e p ro p e r r e g i s t e r s . I f an o p eran d i s n e c e s s a r y , i t i s b ro u g h t i n t o th e m achine from memory®

The com puter i s now p re p a re d to e x e c u te th e command.

B lo ck s 5 -1 1 and 0 r e p r e s e n t th e e x e c u te c y c l e . D uring t h i s c y c le th e o p e r a tio n s p e c i f i e d b y th e i n s t r u c t i o n i s e x e c u te d . A l l a r i t h m e t i c o p e r a tio n s and s h i f t o p e r a tio n s (e x c e p t l e f t b i t s h i f t ) a r e p erfo rm ed b y th e a d d e r i n th e add c y c l e . In th e add c y c l e , b lo c k s 5 -8 , th e o p eran d s a r e combined one o c t a l c h a r a c t e r a t a tim e . The two o c t a l in p u ts to th e a d d e r a r e d e p en d e n t upon th e o p e r a tio n t o be p e r ­ fo rm ed , The r e s u l t i s s t o r e d i n th e a c c u m u la to r,

' B lo ck s 1 2-lij. r e p r e s e n t th e i n t e r r u p t c y c l e , I n th e i n t e r r u p t c y c l e , th e r e g u l a r p rogram i s s to p p e d , th e p la c e w here i t i s s to p p e d i s n o te d , and th e a n a l y s i s c y c le i s s t a r t e d on th e i n t e r r u p t p ro g ram ,

A sim p le d iag ram o f th e flo w o f d a ta w ith in th e com puter i s i l l u s t r a t e d i n F ig u re 1 , 3 , A ll d a ta flo w i n t o o r o u t o f th e com puter m ust p a s s th ro u g h th e S r e g i s t e r ( d i s t r i b u t o r ) . T h is p ro v id e s one in p u t to th e a d d e r . The A r e g i s t e r (a c c u m u la to r) a c t s a s a te m p o ra ry s to r a g e f o r in f o r m a tio n u n t i l th e com puter i s re a d y t o t r a n s f e r th e in f o r m a tio n t o memory. The B r e g i s t e r ( a u x i l i a r y a c c u m u la to r) h o ld s in f o r m a tio n d u rin g th e e x e c u te c y c l e . T h is r e g i s t e r p r o v id e s th e o th e r in p u t t o th e a d d e r . The N r e g i s t e r (command r e g i s t e r ) s t o r e s th e o p e r a tio n code o f th e i n s t r u c t i o n . The L r e g i s t e r (memory a c c e s s r e g i s t e r ) s t o r e s th e a d d re s s o f th e in f o r m a tio n b e in g p ro c e s s e d by

I C o m p l e t e Add

C o m p l e t e Add

1 0

Mem

09 oo

LA Clea

Overf low

M em ^{M e m}

Mem 0 4

LA

O'? 06

A d d

FIGURE 1 .2 COMPUTER CONTROL BLOCK DIAGRAM

L E e q A d d l e M e m o r y

FIGURE 1 .3 COMPUTER DATA FLOW

th e com puter d u rin g e a c h c y c le j th e a d d re s s o f th e i n s t r u c t i o n d u rin g th e f e t c h c y c le and th e a d d re s s o f th e d a ta d u rin g th e e x e c u te c y c le b The LA r e g i s t e r (command c o u n te r ) s t o r e s th e a d d re s s o f th e n e x t s e ­ q u e n t i a l i n s t r u c t i o n * The AC and AD r e g i s t e r s a c t t o g e t h e r to form a I4 b i t c o u n te r . The BC-BD r e g i s t e r s a l s o form a Ij. b i t c o u n te r .

These c o u n te r s a r e u sed t o g a te in p u ts to th e a d d e r and t o th e A r e g - . i s t e r d u r in g an a r i t h m e t i c o r s h i f t o p e r a ti o n . The a r i t h m e t i c u n i t i s a t h r e e - b i t b in a r y a d d e r . I t i s c a p a b le o f r e c e iv in g two o c t a l c h a r ­ a c t e r s and an in p u t c a r r y and p ro d u c in g th e sum w ith c a r r y .

A t th e p r e s e n t tim e , th e com puter h a s a complement o f 13 com­

mands a s f o l l o w s :

ADDit i o n R ing S h i f t A ccum ulator

S U B tra c tio n R ig h t S h i f t and C le a r LoaD A ccum ulator L e f t S h i f t and C le a r STore A ccum ulator L e f t B i t S h i f t

BRanch U n c o n d itio n a lly BRanch on O verflow BRanch on N e g a tiv e B ranch on Non-Zero B ranch on Non-Zero and D ecrem ent

T here a r e s e v e r a l u n u s u a l f e a t u r e s i n t h i s c o m p u te r. The v o l t ­ age l e v e l s a r e v e ry s m a l l. The z e ro l o g i c l e v e l i s z e ro v o l t s j th e one lo g ic l e v e l i s - 2 ,3 3 v o l t s . To o b ta in h ig h sp ee d s w itc h in g a t a low c o s t , th e d e s ig n e r s o f th e com puter made use o f th e in h e r e n t i n ­ d u c ta n c e o f w ire-w ound r e s i s t o r s . The e n e rg y s t o r e d i n th e in d u c ta n c e i s u t i l i z e d t o o v e rd riv e t r a n s i s t o r s o r t o d is c h a r g e r a p i d l y s t r a y o r l i n e c a p a c ita n c e . T h us, h ig h s w itc h in g sp eed s a r e o b ta in e d w ith r e l a ­ t i v e l y sim p le c i r c u i t s .

l s2 ' Tape D riv e

The ta p e d r iv e u t i l i z e d i n t h i s p r o j e c t i s a 727 model I I m an u fa ctu red b y I n t e r n a t i o n a l B u s in e s s M ach in es. The 727 i s no lo n g e r m a n u fa ctu red b u t i s a s ta n d a r d ta p e d r iv e on a l l vacuum tu b e IBM com­

p u t e r s . I t i s d e sig n e d t o p ro v id e s to r a g e f o r l a r g e amounts o f s e ­ q u e n t i a l in f o r m a tio n on m a g n etic t a p e . Power f o r th e e l e c t r o n i c c i r c u i t s and d r iv e m o to rs i s o b ta in e d e x t e r n a l l y , w h ile power f o r th e r e l a y c i r c u i t s i s s e l f - c o n t a i n e d . The f u n c tio n s o f th e ta p e d r iv e a r e w r i t i n g , r e a d in g , b a c k s p a c in g , e r a s i n g , and re w in d in g . In fo rm a­

t i o n i s s to r e d on sev en t r a c k s a c r o s s th e t a p e . Each t r a c k i s i n ­ d e p en d e n t o f th e o th e r t r a c k s , and i s a s s o c ia te d w ith one r e a d / w r i t e h e a d . The ta p e i s fe d th ro u g h th e m achine a t a sp eed o f 75 in c h e s p e r se c o n d . The d e n s i t y o f c h a r a c t e r s i s c o n t r o l l e d b y w r i t e p u ls e s gen­

e r a te d b y an e x t e r n a l s o u r c e . The 727 ta p e d r iv e i s c a p a b le o f r e c o r d ­ in g a maximum 200 c h a r a c t e r s p e r i n c h . In fo rm a tio n may be p la c e d on th e ta p e i n any code d e s i r e d . The i n t e r p r e t a t i o n o f th e in fo r m a tio n i s c o n t r o l l e d by th e e x t e r n a l c i r c u i t r y . The ta p e d r iv e u se s th e

" n o n - r e t u r n - t o - z e r o - i n v e r t e d " (NRZI) sy stem t o re c o r d th e b in a r y i n ­ f o r m a tio n . W ith t h i s s y s te m ,ta p e i s c o n tin u o u s ly s a t u r a t e d i n e i t h e r th e p o s i t i v e o r n e g a tiv e d i r e c t i o n . W ith in any g iv e n p e r io d o f tim e , a change i n s a t u r a t i o n d i r e c t i o n i s c a l l e d a " o n e ," and no change i s c a l l e d a " z e r o ." F ig u re l .U r e p r e s e n t s d a t a and s i g n a l flo w w ith in th e ta p e d r i v e .

urn TT On m T I O ff

6 e l (to lines)

CL 5e

5 el £ I P At LP

Q_

( l lines;

Go

(P (mes) l^vMead

Tape

^ / a v

Unl / F&wer On PeseT T a p e f^reak. Gicjnal

Lot ArriviKjCi L P

---• Load --- ft)inf

FIGURE l.U TAPE DATA FIDW

CHAPTER 2 SYSTEM REQUIREMENTS

2 ,1 Computer

The com puter i s e q u ip p ed w ith a p e r i p h e r a l i n t e r f a c e a d a p t e r , PIA , w hich i s d e sig n e d t o communicate w ith i n p u t / o u t p u t e q u ip m en t.

The PIA c o n ta in s two b u f f e r s , a slow sp eed u n i t and a h ig h sp eed u n i t and a s s o c ia t e d c o n t r o l c i r c u i t s , The h ig h sp ee d b u f f e r c an t r a n s m it and r e c e iv e in f o r m a tio n s im u lta n e o u s ly . I t c o n s i s t s o f two r e g i s t e r s w hich s t o r e sev e n b i t s o f in f o r m a tio n u n t i l th e com puter o r e x t e r n a l

equipm ent i s re a d y t o a c c e p t them .

When th e problem o f com m unication w ith a ta p e d r iv e e x t e r n a l o f th e com puter a r o s e , two s o l u t i o n s w ere c o n s id e r e d . The PIA c o u ld be u sed as a b u f f e r u n i t o r a s e p a r a te u n i t c o u ld be b u i l t . An i n ­ s p e c tio n o f th e PIA re v e a le d two p rim a ry d i f f i c u l t i e s w ith u s in g t h i s m ethod. U sing th e b u f f e r o f th e PIA n e c e s s i t a t e s a com puter program t o assem b le th e 2 5 - b i t com puter w o rd , sev e n b i t s a t a tim e . T h is w ould r e q u i r e more perm an en t s to r a g e i n th e com puter th a n i s d e s i r ­ a b l e , I n a d d i t i o n , th e PIA i s d e sig n e d to a llo w i n t e r r u p t i o n o f th e m ain program o n ly when th e b u f f e r i n d i c a t e s t h a t i t has in f o r m a t io n - to be re a d i n t o th e computer® No f a c i l i t y h as b e e n p ro v id e d to a llo w th e com puter t o a sk f o r in f o r m a tio n . The problem s in v o lv e d i n m o d ific a ­ t i o n o f th e PIA c i r c u i t r y to a llo w i n t e r n a l i n t e r r u p t i o n le d to th e c o n s id e r a ti o n o f th e a l t e r n a t e s o l u t i o n .

10

11

Upon c l o s e r i n s p e c t i o n o f th e s e p a r a te b u f f e r s o l u t i o n , s e v e r a l a d v a n ta g e s w ere found t h a t w ere n o t e v id e n t i n th e i n i t i a l i n s p e c t i o n e By b u i l d i n g a co m p lete new u n i t , th e d e s ig n i s l i m i t e d o n ly b y th e r e ­ q u ire m e n ts o f th e two m achines in v o lv e d and b y th e o p e r a tio n r e q u i r e ­ m ents o T hus, th e o p e r a tio n s a r e n o t l i m i t e d b y th e b u f f e r j th e b u f f e r i s l i m i t e d b y th e o p e r a t i o n s „ The in f o r m a tio n from th e b u f f e r can be g a te d d i r e c t l y i n t o th e S r e g i s t e r and does n o t have t o be assem b led i n th e m ach in e, The o r i g i n a l com puter d e s ig n u t i l i z e d two m em ories„

The p rim a ry memory, m a g n etic c o r e , i s s t i l l u s e d , b u t th e s e c o n d a ry mem­

o ry i s n o t used* The b u f f e r , t h e r e f o r e , can u se th e a d d re s s and th e S r e g i s t e r in p u t l i n e s o f th e se c o n d a ry memory* T h is b u f f e r lo o k s l i k e t h e s e c o n d a ry memory to th e com puter*

2 .2 Tape D riv e

The ta p e d r iv e r e q u i r e s an e x t e r n a l u n i t t o s u p p ly power and c o n t r o l s i g n a l s * The power re q u ire m e n ts o f th e ta p e d r iv e a re a s fo llo w s i 208 v o l t s AC a t 6*0 am peres t h r e e - p h a s e j 236 v o l t s AC re g u ­ l a t e d ; +2 70 v o l t s DC a t 100 m illia m p s ; +II⁴.O v o l t s DC a t 1*5 am p eres;

-6 0 v o l t s DC a t *5 a m p e re s; -1 3 0 v o l t s DC a t 1 0 0 m illia m p s ; -2 70 v o l t s DC a t 100 m illia m p s ; and -s-ljO v o l t s DC a t 200 m illia m p s . The +I4.O v o l t s i s u sed o n ly t o o p e ra te a th e rm a l l i g h t i f th e te m p e ra tu re w ith in th e u n i t becomes e x c e s s iv e * The n o m in al v o lta g e l e v e l s f o r th e ta p e d r iv e a re a s f o l l o w s ; f o r c o n t r o l , -3 0 v o l t s and ^{+ 1 0} v o l t s ; f o r in f o r m a tio n , -1 1; v o l t s f o r a " z e ro " and + 1 0 v o l t s f o r a " one*"

12

The in p u ts and o u tp u ts o f th e ta p e d r iv e a re in d i c a t e d i n F ig u re 1»U. T a b le s I and I I a r e b r i e f d e s c r i p t i o n s o f th e f u n c tio n o f e ach s i g n a l lin e *

2©3 Sequence o f O p e ra tio n s

I n o rd e r t o u n d e rs ta n d hew e ac h s i g n a l i s u t i l i z e d , a d e s c r i p ­ t i o n o f th e sequence o f o p e r a tio n s f o r in p u t and o u tp u t s h o u ld be exam ined,

. F o r an o u tp u t ( w r i t e ) o p e r a t io n , th e fo llo w in g o p e r a tio n s s h o u ld o c c u r . The com puter i n d i c a t e s t h a t i t h as in f o r m a tio n f o r th e ta p e d r iv e to s t o r e . The ta p e s t a r t s moving fo r w a rd . The r e a d /w r ite s t a t u s t r i g g e r i s s e t t o w r i t e s t a t u s and th e S e l , Rea & W rt s i g n a l i s g e n e r a te d , A s i g n a l i s g e n e ra te d when th e in f o r m a tio n t o be s t o r e d i s p r e s e n t a t th e o u tp u t l i n e s o f th e co m p u te r. A l l 2$ b i t s o f th e com puter word a r e t r a n s f e r r e d t o th e o u tp u t r e g i s t e r . From th e r e g ­ i s t e r in f o r m a tio n i s p r e s e n te d t o th e ta p e d r iv e on i t s in p u t l i n e s s e v e n b i t s a t a tim e , and w r it e p u ls e s a re p r e s e n te d on th e W rt P u l l i n e . These w r i t e p u ls e s c o n t r o l th e d e n s i t y o f th e in f o r m a tio n on th e t a p e . The maximum d e n s i t y f o r th e 727 i s 200 b i t s p e r i n c h , w hich r e q u ir e s a 1$ k ilo c y c le w r i t e p u ls e r a t e . D uring th e o u tp u t o p e r a tio n th e in f o r m a tio n b e in g w r i t t e n on th e ta p e a p p e a rs on th e Echo l i n e s f o r a nom inal p e r io d o f 1 0 m ic ro sec o n d s a f t e r th e w r i t e p u l s e ,

The seq u en ce i s c o n tin u e d u n t i l th e com puter i n d i c a t e s t h a t no more in f o r m a tio n i s t o be s t o r e d . A t t h i s tim e th e w r i t e p u ls e s and th e Go l i n e a r e c u t o f f , and a s i g n a l a p p e a rs a t th e W rt LOG l i n e . I n o r d e r f o r th e ta p e t o be c o m p a tib le w ith IBM ta p e u n i t s , th e

13 TABLE I

'l

SIGNAL LINES TO TAPE DRIVE

L ine Symbol F u n c tio n

Go

Backward

S e l e c t

S t a r t Rewind Turn o f f TI

Turn On TI S e t W rite

S t a t u s W rite P u lse

W rite Bus

W rite Check C h a r a c te r S e t Read

S ta tu s

Go

Bwk

S e l

Rew O ff TI

On TI

W rt S t a t u s

W rt P u l

W rt

W rt LCC

Read S t a t u s

C o n tro ls th e s t a r t - s t o p m o tio n o f th e ta p e e

C o n tro ls th e r e v e r s e - f o r w a r d d i r ­ e c t i o n o f ta p e m o tio n .

D eterm in es w hich ta p e d r iv e i s s e l e c t e d i n th e c ase o f m u ltip le ta p e u n i t s ^{( 1 0} lin e s )®

S t a r t s th e rew ind ta p e operation®

Turns o f f th e ta p e i n d i c a t o r l i g h t w hich i s lo c a t e d on th e f r o n t p a n e l o f th e ta p e drive®

T urns on th e ta p e i n d i c a t o r lig h t®

S e ts th e r e a d / w r i t e s t a t u s t r i g g e r t o w r i t e s t a t u s .

C a r r ie s p u ls e s w hich c o n t r o l th e d e n s i t y o f th e c h a r a c t e r s recorded®

C a r r ie s th e in f o r m a tio n to be s t o r e d ^{( 7} lin e s )®

C o n tro ls th e w r i t i n g o f th e lo n g i t u d ­ i n a l check c h a ra c te r®

S e ts th e r e a d / w r i t e s t a t u s t r i g g e r to re a d s t a t u s »

i u TABLE I I

SIGNAL LINES FROM TAPE DRIVE

L ine Symbol F u n c tio n

I n d i c a t e s t h a t th e s e l e c t e d ta p e S e l e c t and A t S e l & LP

Load P o in t

S e l e c t and S e l & Rew Rewind

S e l e c t and S e l & T I O ff TI O ff

S e l e c t and TI On

S e l e c t , Ready and W rite W rite Echo

Bus

S e l e c t , Ready S e l , Rea &

and Read Read

Read Bus Read

d r iv e i s a t th e lo a d p o in t*

I n d i c a t e s t h a t th e s e l e c t e d ta p e d r i v e i s rew in d in g *

I n d i c a t e s t h a t th e ta p e i n d i c a t o r l i g h t on th e s e l e c t e d ta p e d r iv e i s .o f f *

I n d i c a t e s t h a t th e i n d i c a t o r l i g h t i s o n .

I n d i c a t e s t h a t th e s e l e c t e d ta p e d r iv e i s re a d y t o b e g in w r i t i n g . C a r r ie s a p u ls e when a b i t o f in f o r m a tio n i s w r i t t e n on i t s c o rre s p o n d in g t r a c k ( 7 l i n e s ) * I n d i c a t e s t h a t th e s e l e c t e d ta p e d r iv e i s ready, t o b e g in r e a d in g . C a r r ie s th e in f o r m a tio n t h a t i s b e in g re a d o u t ( 7 l i n e s ) .

S e l & TI On

S e l , Rea &

W rt Echo

15

l o n g i t u d i n a l check c h a r a c t e r m ust o c c u r 133 m ic ro sec o n d s a f t e r th e l a s t l i n e o f in f o r m a tio n . When th e ta p e s to p s m oving, th e o u tp u t o p e r a tio n i s c o m p le te . I f , d u rin g an o u tp u t ( w r i t e ) o p e r a ti o n , th e end o f ta p e i s s e n s e d , th e ta p e d r iv e a u to m a tic a lly tu r n s on th e T I and g e n e r a te s a TI On s i g n a l .

F o r an in p u t (r e a d ) o p e r a t io n , th e fo llo w in g o p e r a tio n s s h o u ld o c c u r . The com puter i n d i c a t e s t h a t i t r e q u i r e s in f o r m a tio n from th e ta p e d r i v e . The ta p e s t a r t s moving fo rw a rd , and th e r e a d / w r i t e s t a t u s t r i g g e r i s s e t t o r e a d . The S e l , Rea & Read s i g n a l i s g e n e r a te d .

D ata a re p r e s e n te d t o th e Read b u s a t d i s c r e t e i n t e r v a l s , se v e n b i t s a t a tim e . A s i g n a l i s g e n e r a te d when th e 2 5 - b i t com puter word i s p r e s e n te d to th e in p u t l i n e s o f th e co m p u ter.

When th e in f o r m a tio n r e q u e s te d has b e en re a d from th e ta p e d r i v e , th e l o n g i t u d i n a l ch eck c h a r a c t e r i s p r e s e n te d t o th e Read b u s . A t th e end o f an in p u t s e q u e n c e , th e Go s i g n a l m ust be c u t o f f . T h is

c o m p letes an in p u t o p e r a t i o n .

I n th e above d is c u s s io n s i t s h o u ld be n o te d t h a t th e com puter i s much f a s t e r th a n th e ta p e d r i v e | t h e r e f o r e , i t i s assum ed t h a t th e com puter i s re a d y t o r e c e iv e o r t r a n s m it in f o r m a tio n when th e ta p e d r iv e r e q u i r e s i t t o do s o .

Two o th e r o p e r a tio n s may be i n i t i a t e d by th e co m p u ter, b a c k ­ sp ace and re w in d . The com puter i n d i c a t e s a rew ind o p e r a tio n to th e b u f f e r w hich s i g n a l s th e ta p e d r iv e on th e Rew l i n e . T h is s e t s th e r e a d / w r i t e s t a t u s t r i g g e r to r e a d . When th e rew ind h a s b e en c o m p le te d , th e S e l & Rew s i g n a l i s c u t o f f and th e S e l & LP s i g n a l i s g e n e r a te d .

16

The b a c k sp a c e o p e r a tio n can b e i n i t i a t e d o n ly b y an i n s t r u c ­ t i o n from th e c o m p u ter« When b a c k s p a c in g ? th e Bwk l i n e and th e Go l i n e a r e c u t o n . W henever th e Bwk l i n e i s c u t o f f , th e ta p e w i l l move fo rw a rd i f th e Go l i n e i s o n .

CHAPTER 3 LOGIC DESIGN

The c i r c u i t s o f th e b u f f e r u n i t a r e o rg a n iz e d i n t o f u n c tio n c o n tro l* ta p e c o n tro l* re a d * and w r i t e c i r c u i t s (F ig u re 3 . 1 ) , The f u n c tio n c o n t r o l c i r c u i t s decode c o n t r o l in f o r m a tio n t h a t i s re c e iv e d from th e co m p u te r. T h is in fo r m a tio n in c lu d e s th e s e l e c t in fo r m a tio n and o p e r a tio n in f o r m a tio n . The ta p e c o n t r o l c i r c u i t s c o n t r o l th e op­

e r a t i o n o f th e ta p e u n i t . The r e a d and w r i t e c i r c u i t s p ro v id e in d e ­ p e n d e n t re a d and w r i t e c h a n n e ls t o accommodate s im u lta n e o u s re a d and w r i t e o p e r a tio n s when more th a n one ta p e d r iv e i s u s e d . (A t th e

p r e s e n t tim e o n ly one ta p e d r iv e i s a v a i l a b l e . A d d itio n a l ta p e c o n t r o l c i r c u i t s w ould be n eed ed t o c o n t r o l more th a n one ta p e d r i v e . ) The re a d and w r i t e c i r c u i t s u t i l i z e in f o r m a tio n from th e f u n c t io n c o n t r o l c i r c u i t s t o d i r e c t th e re a d and w r i t e o p e r a t i o n s .

Each main c i r c u i t group i s composed o f a number o f s m a lle r c i r c u i t s * e ac h o f w hich h as a s p e c i f i c f u n c tio n in a g iv e n ta p e o p e r­

a t i o n , The fo llo w in g d i s c u s s io n s p r e s e n t th e o v e r a l l f u n c tio n o f e a c h m ain group and th e n d e s c r ib e th e i n d i v i d u a l c i r c u i t s and th e r o l e e a c h p la y s i n a c c o m p lis h in g group f u n c t i o n s . F ig u re 3 .2 i l l u s t r a t e s th e

l o g i c sym bols u t i l i z e d i n th e s u c c e e d in g f i g u r e s ,

3 ,1 F u n c tio n C o n tro l C i r c u i t s

The f u n c tio n c i r c u i t s r e c e iv e th e i n s t r u c t i o n from th e com puter and decode i t t o d i r e c t th e o p e r a tio n s o f th e b u f f e r unit® T here a r e

17

Input D a ta l?5 i_mes)_______

In p u r D ata l?eadw (l^an^rer)

6 e ( ? LP

f T I OPP On T I 5el f 1 1 Ok?

6 e l <? LP

5el, i2ea, < fe e / O u fp u l (7atd l?eceiv/ej

O u t p u t (7aTa Peady O u tp u t C?5 liioes)______

T ape

C o n tro l Ci rcuite

Ci rcui t s

Ci r c u i i6

FIGURE 3 .1 BUFFER UNIT BLOCK DIAGRAM

IN V

I n v e r t e r

^ r

F l i p - F l o p

3 >

11A n d " G a t e

FIGURE

T

Mote:

T = dels^ tim e

D

' M o t e :

T - t immg

5 6

r "

5 ; n rb

J

ll z-x i'

O r G a t e

3 .2 LOGIC SYMBOLS

H

two decode c i r c u i t s c o n ta in e d i n th e f u n c tio n c i r c u i t . The s e l e c t decode c i r c u i t i s i l l u s t r a t e d i n F ig u re 3 , 3 . T h is c i r c u i t decodes i n s t r u c t i o n b i t s s i x , s e v e n , and e i g h t t o d e te rm in e w h ich ta p e d r iv e th e com puter h as s e l e c t e d . The o p e r a tio n decode c i r c u i t . F ig u re 3oh) d eco d es i n s t r u c t i o n b i t s z e r o , o n e , tw o, t h r e e , and f o u r , t o d e ­ te rm in e th e o p e r a tio n t h a t th e ta p e d r i v e i s t o p e rfo rm ( s e e T able I I I ) ,

3.2 Tape C o n tro l C i r c u i t s

The ta p e u n i t c o n t r o l c i r c u i t s . F ig u re 3 ,5 , c o n t r o l th e d i r e c ­ t i o n and m o tio n o f th e ta p e i n a c c o rd a n c e w ith commands from th e o p e r­

a t i o n decode c i r c u i t s • A s e p a r a te ta p e c o n t r o l u n i t i s r e q u ir e d f o r e ac h ta p e d r i v e . A b a ck sp a ce i n s t r u c t i o n from th e com puter s e t s th e b a c k sp a c e ta p e m o tio n f l i p - f l o p and th e t a p e . d i r e c t i o n f l i p - f l o p . The

" tr u e " o u tp u t o f th e ta p e m o tio n f l i p - f l o p form s th e Go s i g n a l f o r th e ta p e d r i v e . The " t r u e " o u tp u t o f th e ta p e d i r e c t i o n f l i p - f l o p form s th e Backward s i g n a l f o r th e ta p e d r i v e , Four m illis e c o n d s l a t e r , a f t e r th e ta p e h as re a c h e d o p e r a tin g s p e e d , th e b a c k sp a c e re a d s t a t u s f l i p - f l o p i s s e t . T h is form s th e S e t Read S t a tu s s i g n a l f o r th e ta p e d r i v e . A f te r one m illi s e c o n d , th e Read S p ro c k e t s i g n a l i s g a te d i n t o a 266 m icro seco n d r e t r i g g e r a b l e d e la y . The d e la y o f one m illis e c o n d i s t o a llo w th e l o n g i t u d i n a l check c h a r a c t e r t o be p a s s e d o v er w ith o u t a f f e c t i n g th e re a d s p r o c k e t g e n e r a to r . The re a d s p r o c k e t g e n e r a to r , F ig u r e 3 .6 , s im p ly i n d i c a t e s when a l i n e o f in f o r m a tio n i s r e a d . The r e t r i g g e r a b l e d e la y i s r e l e a s e d ^{2 6 6} m ic ro sec o n d s a f t e r th e l a s t l i n e o f in f o r m a tio n i n th e r e c o r d i s r e a d . T h is a c t i v a t e s a U m illis e c o n d

FLO m

Ail lines a r e g a t e d witi?

th e T a p e A d d r e ss s i g n a

FIGURE 3o3 SELECT DECODE CIRCUIT

FLOOIA' IMV

2 ea d

•1021 A

FIGURE 3.1; OPERATION DECODE CIRCUIT

22

TABLE I I I

COMPUTER TAPE INSTRUCTION

O c ta l I n s t r u c t i o n ( f i r s t 10 b i t s ) F u n c tio n

In O l S e a rc h ta p e n

ln 0 3 Read ta p e n

I n^{0 2} W rite ta p e n

l n^{0 6} B ackspace ta p e n

InO k , Rewind ta p e n

23

backspace

J a p e

. Motion

IMV

Turn T I O Track: ^7

Turn TT O ff 5 e l f L P

FIGURE 3 .5 TAPE CONTROL CIRCUITS

FIGURE 3 ,6 READ SPROCKET

ro

25

d e la y w hich a llo w s th e re a d head t o be p o s itio n e d b etw een re c o rd s b e ­ f o r e th e ta p e i s s to p p e d . A f te r th e 1* m illis e c o n d d e l a y , th e ta p e m o tio n f l i p - f l o p and th e ta p e d i r e c t i o n f l i p - f l o p a r e r e s e t . Two hun­

d re d m illis e c o n d s a f t e r th e ta p e m o tio n f l i p - f l o p i s r e s e t , th e re a d s t a t u s f l i p - f l o p i s r e s e t . A t t h i s tim e th e ta p e i s s to p p e d , and th e re a d head i s sp ac e d a p p ro x im a te ly i n th e m id d le o f th e i n t e r - r e c o r d g ap . T h is c o m p le tes th e b a ck sp a ce o p e r a t i o n .

Rewind may be i n i t i a t e d i n two w ay s, A rew ind i n s t r u c t i o n from th e com puter combined w ith th e s i g n a l i n d i c a t i n g t h a t th e ta p e d r iv e is, n o t re w in d in g w i l l s t a r t th e rew in d o p e r a tio n , . T h is o p e r a tio n may a l s o be s t a r t e d a u to m a tic a ll y when th e fo llo w in g c o n d itio n s o c c u r | th e ta p e d r iv e i s n o t re w in d in g , th e ta p e i n d i c a t o r i s on, and th e Go s i g n a l i s o f f , The Rewind s i g n a l , w hich i s g e n e r a te d a u t o m a t i c a l l y , i s d e la y e d

2 0 0 m illis e c o n d s t o a llo w th e ta p e t o s e t t l e i n th e vacuum columns b e ­ f o r e a c c e p tin g a s i g n a l t o change d i r e c t i o n .

The ta p e i n d i c a t o r may be tu r n e d on b y a "one" i n t r a c k number s e v e n when th e ta p e d r iv e i s r e a d in g . I t may be tu r n e d o f f b y th e S e l e c t and a t Load P o in t s i g n a l from th e ta p e d r i v e . The ta p e i n d i c a ­

t o r i s used t o i n d i c a t e an e n d - o f - ta p e c o n d iti o n . In a d d i t i o n , th e ta p e c o n t r o l u n i t s t o r e s th e a d d re s s o f th e ta p e d r iv e w h ich was p r e v ­ i o u s l y u sed o r w hich i s c u r r e n t l y b e in g u s e d ,

3 ,3 W rite C i r c u i t s <

The f u n c tio n o f th e w r i t e c i r c u i t s i s t o a c c e p t 2 5 - b i t compu­

t e r w ords and c o n t r o l th e t r a n s f e r o f t h i s d a ta t o th e w r i t e c i r c u i t s o f th e ta p e d r i v e , The w r i t e o p e r a t io n i s i n i t i a t e d by a com puter

26 in s t r u c t i o n * F ig u re 3*7 i l l u s t r a t e s th e i n d i v i d u a l w r i t e c i r c u i t s and t h e i r r e l a t i o n t o e a c h o th e r*

O u tp u t r e g i s t e r * The o u tp u t r e g i s t e r c o n s i s t s o f 2$ f l i p - f l o p s t o s t o r e th e 2 5 - b i t com puter word* Only th e " tr u e " in p u ts a r e u sed t o t r a n s f e r in f o r m a tio n i n t o th e r e g i s t e r , and th e s e in p u ts a r e g a te d w ith a t r a n s f e r d a ta s i g n a l from th e w r ite c o n t r o l c i r c u i t * The f l i p - f l o p s a r e r e s e t p r i o r t o th e t r a n s f e r o f a word i n t o th e r e g i s t e r *

D isassem b ly c i r c u i t s * The d is a s s e m b ly c i r c u i t s . F ig u re 3*8, c o n s i s t o f a d is a s s e m b ly m a tr ix and a w r i t e r e g i s t e r * The d is a s s e m b ly m a trix s e q u e n t i a l l y e x t r a c t s each ⁵- b i t c h a r a c t e r from th e o u tp u t

r e g i s t e r and p r e s e n ts i t t o th e w r i t e r e g i s t e r in p u ts * T h is e x t r a c t i o n i s c o n t r o l l e d b y th e d is a s s e m b ly c o u n te r* The lo w e s t- o r d e r c h a r a c t e r i n th e o u tp u t r e g i s t e r i s e x t r a c t e d f i r s t , th e n e x t lo w e s t- o r d e r s e c o n d , e tc * The w r i t e r e g i s t e r c o n s i s t s o f f i v e f l i p - f l o p s w hich h o ld each l i n e o f d a ta a s i t i s b e in g re c o rd e d on th e ta p e * The i n p u ts t o th e w r i t e r e g i s t e r a re g a te d w ith a t r a n s f e r d a ta s i g n a l from th e w r ite c o n t r o l c i r c u i t * The w r i t e r e g i s t e r i s c le a r e d p r i o r t o th e t r a n s f e r o f d a t a i n t o th e r e g i s t e r *

D isasse m b ly C o u n te r* The d is a s s e m b ly c o u n te r i s a s ta n d a r d modulo 5 c o u n te r (F ig u re 3 . 9 ) . The c o u n te r c o n tr o ls th e d is a s s e m b ly ; o f 2 5 - b i t com puter w ords i n t o f i v e 5 - b i t c h a r a c te r s * The o u tp u t o f th e c o u n te r i s i n t e r r o g a t e d a t th e end o f a w r i te o p e r a tio n t o d e t e r ­ mine i f th e number o f l i n e s re c o rd e d was an i n t e g r a l m u l tip l e o f f iv e * The c o u n te r i s o p e ra te d b y p u ls e s from th e w r i t e c o n t r o l c i r c u i t s * I t i s r e s e t t o a e ro a t th e s t a r t o f a w r i t e sequence b y a s i g n a l from th e w r i t e c o n t r o l c i r c u i t s *

In^frucii_{— ■»} Function ConlroJ Clneck Rinty

O u i p u t C b t a

f? e a d y Q u tp u l

deceived

Transfer Dild

to (Xipur ireq

O utp ut lines)

W rite 5e (e c7

W n t e

Farit/

C h e c k

W rite

CoKif’ro

Circuits

Advance Counter C hecb jengtio C le a r W r t l?e

LI e a r w rr Ice^_______

T r a n s f e r CWa To Wrt &

Clear Wrf &

Cel fTI On

O u tp u t Register

E~clno Q I m o )

5el {LP 5el ? Cei

Wrt P e ady

' 5 e U T l On

W rt ICC

Wrt Ful Wrt Go

DiSdSSCntph

D lS tiS S em k ly Vl/ri ( l lines)

FIGURE 3 .7 WRITE CIRCUIT BLOCK DIAGRAM ^ro

28 ‘

* 1 0

CT/Z- 2

J Z l A2 2,

*ZL J Z L CTI2- o

0 2 ^{* 1}

*2

*1 H

*5 _h

CT(? = I

#7

* 8

# 9

ToUJt-t P e a

=[>

Ml M2

*15

*14

*15

D

= n >

*l(e

± n

*18

*/9

*%>

C T I Z =4.

d -

=D

6

Trdnsfch Rid

CH

Clear

Ujr V I?fl^

T

e F

5 T

z F

5 T

12 F

FIGURE 3 .8 DISASSEMBLY CIRCUITS

C lear

FIGURE 3 .9 MODULO $ COUNTER

30

P a r i t y g e n e r a t o r . Each l i n e re c o rd e d on th e ta p e i s composed o f a 5- b i t c h a r a c t e r , a p a r i t y b i t , and an e n d - o f - ta p e b i t f o r . a t o t a l o f sev e n b i t s . The p a r i t y g e n e r a to r . F ig u re 3 .1 0 , makes th e t o t a l number o f " one" b i t s i n a l i n e odd f o r c o m p a ta b ility w ith th e IBM f o r m a t. The p a r i t y b i t i s s t o r e d i n th e p a r i t y f l i p - f l o p and then, w r i t t e n ; i n ■ t r a b k r;six o n h th e : ta p e „ .

W rite p a r i t y c h e c k . The w r i t e p a r i t y c h e c k . F ig u re 3 .1 1 , d e­

te rm in e s i f a p a r i t y e r r o r h a s o c c u rre d d u rin g a w r i t e o p e r a ti o n . T his ch eck i s p erfo rm ed on th e W rite Echo s i g n a l s from th e co m p u te r. I f an e r r o r o c c u r s , th e w r it e p a r i t y e r r o r f l i p - f l o p i s s e t . The w r i t e p a r ­ i t y ch eck i s p erfo rm ed on e v e ry l i n e t h a t i s w r i t t e n e x c e p t th e l o n g i ­ t u d i n a l check c h a r a c t e r .

W rite c o n t r o l . The w r i t e c o n t r o l c i r c u i t s c o n ta in two s e p a ­ r a t e c i r c u i t s ; th e w r i t e ta p e m o tio n c i r c u i t . F ig u re 3 .1 2 , and th e w r i t e tim e sequence c i r c u i t , F ig u re 3 .1 3 .

The w r i t e ta p e m o tio n c i r c u i t i s a c t i v a t e d b y a w r i t e i n s t r u c ­ t i o n from th e c o m p u ter. I f th e s e l e c t e d ta p e u n i t i s a t th e lo a d p o i n t , a 2 0 0 m illis e c o n d d e la y o c c u rs b e f o r e th e ta p e m o tio n f l i p - f lo p i s s e t t o s t a r t th e ta p e m oving; i f th e ta p e i s n o t a t th e lo a d p o i n t , th e f l i p - f l o p i s s e t im m e d ia te ly . The 200 m illi s e c o n d d e la y a llo w s tim e f o r th e ta p e t o s t a b i l i z e i n th e vacuum columns when a rew ind o p e r a tio n i s co m pleted im m e d ia te ly p re c e d in g a w r i t e s e l e c t i o n . The s e t t i n g o f th e ta p e m o tio n f l i p - f l o p i n t u r n s e t s th e w r i t e s t a t u s f l i p - f l o p a f t e r a s h o r t d e la y . T h is d e la y i s 80 m illis e c o n d s i f th e s e l e c t e d ta p e d r iv e i s a t th e lo a d p o i n t and U m illis e c o n d s i f i t i s n o t a t th e lo a d p o i n t . When th e ta p e d r iv e i s a t th e lo a d p o i n t .

INV

- ) “ L

*3

IMV

-I IN\/

h

&

- ) - L

W ~ T -

■T W

S e t f T I O n

IMV

FIGURE 3 .1 0

5 T

End o f

Tract:

* 1

Clear

Wrt I?ea g F —

PARITY GENERATE CIRCUITS

Echo*

INV

TWV

W

I M

Error

TW M

f W

FIGURE 3 c l l WRITE PARITY CHECK CIRCUITS

VJrf Q

~U7rf be _{Wrt Ft}

FIGURE 3<,12 WRITE TAPE MOTION CIRCUITS

VjJVu

End W rite

Write Status

S e —S E U —

\iin~ 5fa PP

D

1 2e^

FIGURE 3 .1 3

Cl ear Wrt I?ecj

CTIZ = 0

O

Oof pot £?e^

2 7 s e c

CTf2=0

5CC

CTE- 0

fQ/> sec

Transfer- Qgla To Wrt Lecj O u tp u t Datd [?ecei\/ed

Pulse Wrt Ckts Adv .ere ^

Ckeclc l%ri t Y

Clear Output y P e a

WRITE TIMING SEQUENCE CIRCUIT

35

th e 8 0 m illis e c o n d s d e la y a llo w s th e r e f l e c t i v e s p o t on th e ta p e t o move p a s t th e w r i t e head b e f o r e w r i t i n g b e g in s . A p p ro x im a te ly s i x

in c h e s o f ta p e m ust p a s s th e w r ite heads b e f o r e w r i t i n g b e g in s t o p r o v id e c o m p a t i b i l i t y w ith IBM equipm ent ( s e e F ig u re A .3 f o r ta p e f o r ­ m a t) . The U m illi s e c o n d s d e la y a llo w s tim e f o r th e ta p e t o re a c h

o p e r a tin g speed b e fo re w r i t i n g b e g in s and f i x e s th e l e n g th o f th e i n t e r - r e c o r d g a p . The o u tp u t o f th e w r i te s t a t u s f l i p - f l o p i s u sed a s th e S e t W rite S t a tu s s i g n a l f o r th e ta p e d r iv e and a s th e s t a r t i n g s i g n a l f o r th e w r i t e tim in g s e q u e n c e .

The end o f a w r i t e o p e r a tio n i s d e te c te d b y an end w r i t e s i n g l e s h o t . T h is s i n g l e s h o t i s t r i g g e r e d e ach tim e a word i s re a d y to be t r a n s f e r r e d t o th e b u f f e r u n i t . I f no word i s t o be t r a n s f e r r e d , th e w r i t e p u ls e s a re n o t g a te d to th e ta p e d r i v e , and th e r e t r i g g e r a b l e d e la y i s n o t t r i g g e r e d . A f te r a 266 m icro seco n d d e la y , th e l o n g i t u d i n ­ a l check c h a r a c t e r i s w r i t t e n j and a f t e r an a d d i t i o n a l 1* m illi s e c o n d s , th e ta p e m o tio n f l i p - f l o p i s r e s e t . A f te r an a d d i t i o n a l 200 m i l l i ­ s e c o n d s , th e w r ite s t a t u s f l i p - f l o p i s r e s e t and t h e d is a s s e m b ly c o u n t­

e r i s checked f o r a l e n g t h e r r o r . T h is co m p letes th e w r i t e o p e r a t io n . The w r i t e tim in g sequ en ce c i r c u i t s c o n t r o l a l l th e w r i t e o p e r­

a t i o n s . The o u tp u t r e g i s t e r i s c le a r e d i n i t i a l l y when th e w r i t e s t a t u s f l i p - f l o p i s set® The w r i t e s t a t u s " t r u e ” s t a r t s a 15 k i l o ­ c y c le c lo c k . The p u ls e s o u t o f th e c lo c k a r e g a te d w ith th e End W rite f s i g n a l t o p e rfo rm s e v e r a l f u n c t i o n s . The w r it e r e g i s t e r i s c l e a r e d , and d a ta a r e t r a n s f e r r e d t o th e o u tp u t r e g i s t e r i f th e d is a s s e m b ly c o u n te r i s z e r o . A f t e r a ^{2 2} m icro seco n d d e la y , f i v e b i t s o f th e word a r e t r a n s f e r r e d t o th e w r i t e r e g i s t e r . I f th e d is a s s e m b ly c o u n te r i s z e r o , th e O u tp u t D ata R eceiv ed s i g n a l i s g e n e r a te d . A f t e r a n o th e r 22

36

m icro seco n d d e la y , th e w r i t e c i r c u i t s a r e p u ls e d , th e w r i t e p a r i t y i s c h ec k e d , and th e d is a s s e m b ly c o u n te r i s p u l s e d „ A f t e r a 10 m ic ro ­ seco n d d e la y and i f th e c o u n te r i s z e r o , th e o u tp u t r e g i s t e r i s c le a re d o The seq u en ce keeps r e p e a tin g u n t i l th e End W rite s i g n a l i s c u t o ffo

3<>U Read C i r c u i t s

The f u n c tio n o f th e re a d c i r c u i t s i s t o assem b le in fo r m a tio n from th e ta p e i n t o 25- b i t com puter w ords and t o c o n t r o l t r a n s f e r o f th e s e w ords t o th e computer® T h is f u n c t i o n i s in v o lv e d i n two o p e ra ­ t i o n s r th e s e a r c h o p e r a tio n and th e re a d o p eration® These o p e r a tio n s a r e i n i t i a t e d b y com puter i n s t r u c t i o n s „ F ig u re 3 . lit i l l u s t r a t e s th e i n d i v i d u a l re a d c i r c u i t s and t h e i r r e l a t i o n t o e a c h other®

In p u t r e g i s t e r ® The in p u t r e g i s t e r c o n s i s t s o f 2$ f l i p - f l o p s t o s t o r e th e assem b led com puter w o rd . Only th e ” t r u e ” b i t s a r e u sed ? t o t r a n s f e r in fo r m a tio n i n t o o r o u t o f th e r e g i s t e r . The " tr u e " o u t­

p u ts o f th e r e g i s t e r a r e g a te d w ith a t r a n s f e r d a t a s i g n a l f o r in p u t to th e c o m p u ter. The f l i p - f l o p s a re r e s e t p r i o r t o th e t r a n s f e r o f th e f i r s t 5- b i t s o f in f o r m a tio n i n t o th e r e g is te r ®

A ssem bly c i r c u i t s ® The assem b ly c i r c u i t s . F ig u re 3®l5, con­

s i s t o f an asse m b ly m a trix and a re a d r e g i s t e r . The assem b ly m a trix s e q u e n t i a l l y i n s e r t s e ac h 5- b i t c h a r a c t e r i n t o th e i n p u t r e g i s t e r from th e g a te d o u tp u ts o f th e r e a d re g is te r ® The o u tp u ts o f th e re a d r e g i s ­ t e r a r e g a te d w ith a t r a n s f e r d a ta sig n al® The a sse m b ly i s c o n t r o l l e d b y th e assem b ly c o u n te r . The lo w e s t- o r d e r c h a r a c t e r i s i n s e r t e d f i r s t ,

th e n e x t lo w e s t- o r d e r se c o n d , e t c . The re a d r e g i s t e r c o n s i s t s o f f i v e

In p u t (25 lines]

Cnecic fenfc

Clear .

5eU 2e

Q_

(?ead

ro

FIGURE 3 . m READ CIRCUIT BLOCK DIAGRAM ^{V )}

38

Inpiri *1 ^{C T fcO} Transfer Ua\a t o I n p o t £ e q ,,

" T ^

T ra n Paid to l?ead

Lead ?ea

CTfcZ

sC

FIGURE 3 .1 5 ASSEMBLY CIRCUITS

39

f l i p - f l o p s w hich r e c e iv e e ac h l i n e o f in fo r m a tio n from th e ta p e d r iv e d u rin g a re a d o r s e a r c h o p e r a t i o n » The o u tp u ts from th e ta p e d r iv e a r e g a te d w ith a t r a n s f e r d a ta s i g n a l t o form th e in p u t s t o th e re a d r e g i s t e r s The re a d r e g i s t e r f l i p - f l o p s a r e c le a r e d p r i o r t o an y t r a n s ­ f e r o f in f o r m a tio n i n t o th e r e g i s t e r .

A ssem bly c o u n te r . The asse m b ly c o u n te r i s c o n s tr u c te d i d e n t i ­ c a l l y t o th e d is a s s e m b ly c o u n te rs I t c o n t r o l s th e asse m b ly o f f i v e 5 - b i t c h a r a c te r s i n t o 2 5 - b i t com puter w o rd s. The o u tp u t o f th e c o u n te r i s i n t e r r o g a t e d a t th e end o f a re a d o p e r a tio n t o d e te rm in e i f th e num­

b e r o f l i n e s re a d was an i n t e g r a l m u ltip l e o f f i v e . The c o u n te r i s o p e ra te d b y p u ls e s from th e re a d c o n t r o l . I t i s r e s e t t o z e ro a t th e s t a r t o f a re a d o r s e a rc h o p e r a tio n by a s i g n a l from th e re a d c o n t r o l c i r c u i t s .

Read s p r o c k e t. The re a d s p r o c k e t , F ig u re 3 ,6 , g e n e r a te s a s i g ­ n a l w henever a l i n e o f in fo r m a tio n i s re a d b y th e ta p e d r i v e . S in c e th e t o t a l number o f "one" b i t s in any g iv e n l i n e m ust be o d d , th e sim p le " o r" c i r c u i t g e n e r a te s a s i g n a l w henever a l i n e o f in f o r m a tio n a p p e a rs a t i t s i n p u t s . The re a d s p r o c k e t i s u sed to s i g n a l th e end o f a r e c o r d .

Read p a r i t y c h e c k . The re a d p a r i t y check c i r c u i t . F ig u re 3 .1 6 , c o n s i s t s o f two f l i p - f l o p s and l o g i c to d e te rm in e w h e th e r th e t o t a l num­

b e r o f "one" b i t s i n any l i n e i s odd o r e v e n . The two f l i p - f l o p s a r e n e c e s s a r y to s t o r e th e in f o r m a tio n from tr a c k s s i x and s e v e n . I f th e p a r i t y ch eck s e v e n , a re a d p a r i t y e r r o r f l i p - f l o p i s s e t . The re a d p a r i t y ch eck i s p erfo rm ed on e v e r y l i n e t h a t i s re a d e x c e p t th e l o n g i ­ t u d i n a l check c h a r a c t e r .

IKJV

IKJV

m

I N V

Traci: T racL

Clear

Dn

4 INiV 1—

FIGURE 3 .1 6 REA.D PARITY CHECK CIRCUITS

t rO