Hybrid Computing at Ames Research Center: The Ames Linkage System and the Digital Logic Simulator
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~ & 5 4 t h e s Research Center
Ploffett Field, C a l i f o r n i a
ISTRODUCTIOJ
It has been our p r i v i l e g e a t t h e Ames Research Center t o
be a b l e t o p a r t i c i p a t e i n t h e design and development of two
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advanced hybrid computing machines, t h e Ames Linkage System
and t h e D i g i t a l Logic Simulator.
l
The Ames LiEkage System was b u i l t around requirements of
a s p e c i f i c s i m u l a t i o n , and because of t h e magnitude pf t h e
mission, t h e u n i t was designed p r i m a r i l y t o f i t t h e s e s p e c i f i c a t i o n s .
The unusual f e a t u r e s of t h e linkage a r e emphasized along w i t h a
g e n e r a l d i s c u s s i o n of i t s c a p a b i l i t i e s .
The D i g i t a l Logic Simulator w a s developed f o r a i d i n g i n
che e x p e d i t i o u s s o l u t i o n of s i m u l a t i o n problems c o n t a i n i n g l o g i c
elements.
However, a wide v a r i e t y of i n t e r e s t i n g a p p l i c a t i o n s
of t h i s device have been worked out a t t h e Center and it i s f e l t
i
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t h a t t h e s e a p p l i c a t i o n s i n d i c a t e t h e f u t u r e p o t e n t i a l i t i e s of
t h i s c l a s s of machine.
Three recent a p p l i c a t i o n s w i l l be discussed
i n some d e t a i l .
The Ames Linkage System
~
When approaching t h e problem of s i m u l a t i n g r e e n t r y v e h i c l e s
over t y p i c a l f l i g h t p r o f i l e s .in the e a r t h s atmosphere, t h e
f o r computation of t h e v a r i o u s
inadequacies of t h e anaiog computer
I f one f u r t h e r
n a v i g a t i o n parameters become very troublesome.
contemplates space n a v i g a t i o n s i m u l a t i o n , t h e analog mechanization
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.
.
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1
.
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computational f a c i l l t y t h a t could s a t l s f a c t o r i i y reproduce
t h e f l i g h t c h a r a c t e r i s t i c s of space v e h i c l e s .
S e v e r a l major f a c t o r s shaped t h e design of t h e linkage:
1)
P h y s i c a l s e p a r a t i o n of t h e analog and d i g i t a l
facilities ,
2)
Necessity f o r conservation of d i g i t a l compcter time
f o r economic reasons ,
3)
Control and o p e r a t i o n of t h e l i n k a g e i n v e s t e d i n a
remote s i m u l a t i o n machine,
4)
Extensive readout of d i g i t a l computer v a l u e s d i r e c t l y
on s i m u l a t o r c o n t r o l p a n e l s .
Figure 1 shows g r a p h i c a l l y t h e p h y s i c a l s e p a r a t i o n of t h e t w o
computer f a c i l i t i e s .
The analog computer, t h e l i n k a g e eciuipment,
and s i m u l a t i o n machine a r e l o c a t e d i n t h e b u i l d i n g i n t h e upper
,
r i g h t hand p o r t i o n of t h e f i g u r e and t h e d i g i t a l f a c i l i t i e s i.n
t h e b u i l d i n g a t t h e lower l e f t hand p o r t i o n of t h e f i g u r e .
The
white l i n e shows t h e 2500 f t . path of t h e underground conduit
t h a t c o n t a i n s t h e 73 coax t r a n s m i s s i o n l i n e s t h a t make t h e s i g n a l
connections between t h e t w o computers.
Digital s i g n a l transmission
appeared t h e most d e s i r a b l e method of communication from t h e o u t s e t ,
but whether t r a n s m i s s i o n of s a t i s f a c t o r y d i g i t a l wave shapes over
t h i s d i s t a n c e could be achieved was of paramount importance t o t h e
system design.
The 7 3 l i n e s permit p a r a l l e l 16 b i t p l u s s i g n d a t a
word and p a r a l l e l 10 b i t sense word c o m u n i c a t i o n i n both d i r e c t i o n s
simultaneously.
While t h i s system concept r e q u i r e d more w i r e l i n e s ,
i t greaLly s i m 2 l i f i e d t h e final. l i n k a g e hardware.
Serial
t r a n s m i s s i o n w a s considered, but t h e d a t a r a t e s and equlpment
c o m p l l c a t i o c s e l i m i n a t e d t h i s mode of o 2 e r a t i o n .
T.l.
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-39
an
.
economic viewpoint, i t makes very l i t t l e c l i f f e r e i c e i f one o r
100 t r a n s m i s s i o n l i n e s a r e used s i n c e s e r i a l trans:..ission
r e q u i r e s a d d i t i o n a l l o g i c , higher speed l o g i c , and more e n g i n e e r i n g
design time t h a n &v r a l l e l
transmission.
The c a b l e s l i e i n s a l t
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water through much of t h e y e a r , t h e r e f o r-.re , ’ R G 62 A/U c a b l e was
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each lire beingj$500 f t . long s o t h a t no i n t e r m e d i a t e
used
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connectors a r e r e q u i r e d .
Figure 2 shows t h e r e s u l t s of a t e s t , r u n by Packard B e l l
Computer Corporation, t o show the e l e c t r i c a l performance of t h e
f i n a l t r a n s m i s s i o n system.
The t r a n s m i s s i o n system, which senses
t h e c u r r e n t mode of t h e l i n e , r e q u i r e s t r a n s m i s s i o n l i n e d r i v e r s
I
between t h e i n p u t s t a g e and t h e l i n e .
Line r e c e i v e r s and p u l s e
shapers a r e r e q u i r e d between t h e o u t p u t of t h e l i n e and Lne o u t p u t
s t a g e f o r successful operation.
Figure 2 shows t h e d i s t o r t i o n s
~
of t h e a c t u a l t r a n s m i t t e d s i g n a l s and. c o r r e c t i o n s e f f e c t e d by
p u l s e r e s h a p e r s i n t h e transmission l i n e r e c e i v e r u n i t s .
.
The 5 p s e c .
of d e l a y shown by t h e oscillogram i s introduced by t h e l i n e l e n g t h
and t h e v e l o c i t y of propagation c h a r a c t e r i s t i c s of t h e t r a n s m i s s i o n
cable.
Operational experience with t h i s d i g i t a l t r a n s m i s s i o n l i n k
h a s been very s a t i s f a c t o r y , w i t h m i l l i o n s of words having been
t r a n s m i t t e d e r r o r f r e e i n both d i r e c t i o n s .
To permit a computer t o s t a n d i d l e i s viewed as a f e l o n i o u s
o f f e n s e i n a high p r e s s u r e d i g i t a l computer l a b o r a t o r y .
Therefore,
t h e i n t r o d u c t i o n of a linkage system t o connect on a f l i g h t
s i m u l a t o r with i t s myriads of people, problems, and delays i s
viewea w i t h SC.T.:*
j u s t i f i a b l e apprehension by t h o s e r e s p o n s i b l e f o r
e f f e c t i v e u t i l i z a t i o n of t h e d i g i t a l equipment.
T’nerefore, a
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c o n s i d e r a b l e e f f o r t has been expended t o develop a method of
e f f i c i e n t l y i n t e r r u p t i n g t h e normal d i g i t a l computer o p e r a t i o n s
f o r f l i g h t s i m u l a t i o n computations on a demand bas-3.
A Data Acceptance Routine (DAR) has been implemenzed and i s
shown i n flow diagram form i n Figure 3 .
The major p o i n t s of t h e
r o u t i n e are:
1)
Routine permanently s t o r e d i n computer c o r e ,
Routine permits i n p u t i n g of d a t a from s i m u l a t i o n with
only a momentary h a l t i n g of d i g i t a l computer.
3)
Routine permits e f f i c i e n t i n t e r l a c i n g of production
work w i t h s i m u l a t i o n work, w i t h s i m u l a t i o n given p r i o r i t y .
The o b j e c t of t h e r o u t i n e i s t o keep t h e d i g i t a l i n
production o p e r a t i o n u n t i l t h e moment a f l i g h t s i m u l a t i o n begins.
S i m i l a r l y , a t t h e t e r m i n a t i o n of a s i m u l a t i o n r u n , t h e d i g i t a l
equipment i s r a p i d l y r e t u r n e d t o production work.
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changeover time i s A0 seconds.
The maximum
The major p o i n t of i n t e r e s t i n t h e d a t a acceptance r o u t i n e i s
t h a t d a t a can be t r a n s m i t t e d t o t h e s i m u l a t i o n program without
dumping t h e production program. The key t o t h i s procedure i s t h e
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f a c t t h a t t h e d i g i t a l A c a n perform a l l t h e o p e r a t i o n s of t h e DAR,
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i n c l u d i n g t e s t i n g f o r a compute code without d i s t u r b i n g 4
3
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arithmetic register.
The conversion components of t h e l i n k a g e such as t h e
m u l t i p l e x e r ( M P X ) , analog t o d i g i t a l c o n v e r t e r (ADC), and t h e
d i g i t a l - t o - a n a l o g c o n v e r t e r (DAC) a r e a l l s t a n d a r d items of t h e
1,233
15 KC, 13 b i t p l u s s i g n b i t c l a s s and do not need any ex2lznation.
F i g u r e 4 shows a s i m p l i f i e d block diagram of t h e s i g n a l p a t h s
between t h e d i g i t a l and analog p o r t i o n s using t h e co;,version
~.xc.n;x d i r e c t
The s e n s e output l i n e s 05 the c I C g i ~ ~ 2 .
components.
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t h e channel s e l e c t i o n of t h e D.4C and ADC u n i t s p e r m i t t i n g random
s e l e c t i o n of t h e ADC and DAC channels.
Figure 5 i s a photograph of t h e p i l o t s c o n t r o l panel of t h e
r e e n t r y v e h i c l e being simxlated.
O f p r i n c i p a l concern h e r e a r e
t h e computer d i s p l a y panel (upper r i g h t ) and t h e keyboard p a n e l .
The c o n t r o l panel permits o p e r a t i o n a l c o n t r o l of t h e e n t i r e
’
linkage-computer system.
The f l o w of data t o t h e d i g i t a l ’ c o m p u t e r
from both analog and p i l o t i n p u t s i s shown diagrammatically i n
Figure 6.
I n a d d i t i o n t o d i g i t i z e d d a t a from t h e ADC, t h e v e h i c l e
p i l o t has t h e a b i l i t y t o input d i g i t a l information through t h e
keyboard panel v i a t h e d i g i t a l input d a t a l i n e s .
The fuiiction o f
t h e check d i s p l a y on t h e computer d i s p l a y panel i s t o g i v e t h e
p i l o t a v i s u a l i n d i c a t i o n of h i s manual d a t a i n p u t .
Operational
i n s t r u c t i o n s a r e e n t e r e d i n t o the system by t h e l a r g e pushbuttons
on t h e keyboard p a n e l v i a t h e sense i n p u t l i n e s .
The d a t a flow from t h e d i g i t a l computer i s i i i u s t r a t e d i n
Figure 7.
The sense o u t p u t codes address t h e c o n t r o l panel
s e l e c t o r on t h e ADC-DAC channel s e l e c t o r .
This determines whether
t h e information from t h e d a t a output l i n e s a r e transmicted t o
t h e d i s p l a y s o r t o t h e DAC u n i t s .
Figures 6 and 7 i l l u s t r a t e t h e
e x t e n s i v e d i g i t a l communication l i n k between t h e s i m u l a t o r and t h e
d i g i t a l computer.
The most potent use f o r t h i s d i s p l a y c a p a b i l i t y
i s during space f l i g h t p o r t i o n of t h e mission s i m u i a t i o n .
Here
a l s o maximum advantage of t h e Data Acceptance Routine can be seen,
f o r d u r i n g midcourse phases only o c c a s s i o n a l use of t h e s i m u l a t i o n
computer i s needed f o r t h e n a v i g a t i o n a l phase of a space f l i g h t .
C a l l up times of only s e v e r a l seconds p e r 15 minute i n t e r v a l s
a r e r e q u i r e d d u r i n g midcourse navigation.
The r e e n t r y phase requirements on combiced computer systerns
a r e s u b s t a n t i a l l y d i f f e r e n t froin t h o s e of midcourse phase.
P r i m a r i l y , t h i s occurs because aerodynamics of t h e v e h i c l e a r e
added t o t h e p a r t i c l e dynamics of t h e midcourse phase.
'
From t h e
computer viewpoint, continuous o p e r a t i o n of b o t h t h e d i g i t a l and
analog p o r t i o n s a r e r e q u i r e d , with heavy dependance on t h e analog
'
f o r s h o r t p e r i o d modes of t h e simulation.
While a d e t a i l e d
d i s c u s s i o n of t h e r e e n t r y mechanization i s beyond t h e scope of
t h i s paper, a b r i e f d i s c u s s i o n i s of i n t e r e s t .
The e n t i r e r e e n t r y
mission i s approximately of 15 minutes d u r a t i o n and t h c d i g i t a l
computer must be on l i n e continuously.
For t h i s r e a s o n , many of
t h e advantages of che DAR a r e not used, p a r t i c u l a r l y th;
o f d a t a w h i l e doing p r o d u c t i o n work.
inputing
T h e r e f o r e , only t h e e x i t
p o r t i o n of t h e DAR i s used i n t h e r e e n t r y phase.
Figure 8 i s a flow diagram of t h e computer o p e r a t i o n f o r t h e
r e e n t r y phase.
The s i m u l a t i o n program i s loaded i n t o the d i g i t a l
computer as s t a n d a r d p r o d u c t i o n program.
The s i m u l a t i o n o p e r a t o r
a c t u a t e s t h e I.C. pushbutton and t h e d i g i t a l sends t h e I.C. v a l u e s
t o the a n a l o g , a n d goes, a u t o m a t i c a l l y , o f f l i n e .
AfCer t h e check-
o u t of t h e s i m u l a t o r i s completed, t h e s i m u l a t i o n must be rei n s t a t e d , by p r o d u c t i o n methods, i n t o t h e d i g i t a l c o m p u t a .
o p e r a t e c y c l e t h e n commences as shown on t h e c h a r t .
The
This c o n t i n u e s
u n t i l e i t h e r t h e I.C. o r H a l t pushbuttons are a c t u a t e d which
a u t o m a t i c a l l y e x i t s t h e d i g i t a l computer.
The system of e q u a t i o n s emp'dyed i n t h i s r e e n t r y phase are
t h o s e devised by F o r g a r t y and Howe of t h e U n i v e r s i t y of Michigan.
4
T h i s system, c a l l e d thz Nodified F l i g h t P a t h Axis System, i n t r o d u c e s
several s p e c i a l a x i s frames, two of which need e x p l a n a t i o n f o r t h i s
discussion.
These two fraines a r e c a l l e l t h e ._ -.:me
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aid 3 i'rame.
v e h i c l e ; t h e v e c t o r components p o i n t n o r t h , e a s t and down.
The
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The Ames D i g i t a l Logic S i m u l a t o r ;2LS)
o p e r a t i o n d u r i n g September 1962.
was pLacsd in
Since t h a t time i t has
r e c e i v e d c o r s i d e r a b l e a t t e n t i o n from p r o s p e c t i v e u s e r s of
s i m i l a r equipments as t o t h e u s e f u l n e s s of l o g k a l coq2uting
elements i n an analog s i m u l a t i o n l a b o r a t o r y .
The o r i g i n a l impetus f o r the DLS w a s a simLAation
requirement f o r a i d i n s t u d y i n g a n e a r t h o r o i t s a t e l l i t e
c a l l e d 0. G. 0. ( O r b i t i n g Geophysical Observatory).
It w a s
most: troublesome t o provide proper s i m u l a t i o n of t h e r e a c t i o n j e t c o n t r o l l e r s ar,d t h e l o g i c a l a u t o p i l o t system w i t h s t a n d a r d
analog components.
For i n s t a n c e t h e analog mechzatzatioc of
l o g i c c o n t r o l l e r s took some 400 d i o d e s , 135 art;;,Lfiers,
t h e O.G.O.
and two s p e c i a l l y f i t t e d EA1 3 1 R p a t c h p a n e l s .
The s p e c t r e of
having t o r e p e a t t h i s p r o c e s s r e s u l t e d i n a c o n t r a c - award t o
E l e c t r o n i c s A s s o c i a t e s t o develop t h e DLS, known commerciLlly
today as t h e EA1 DOS 350.
The DLS w a s designed t o be a n accessory t o z k z anaiog simLLation
computers.
It w a s , t h e r e f o r e , equipped t o e a s i l y connect i n t o
and f u n c t i o n w i t h s t a n d a r d r e a l time analog computers.
As
p r e s e n t l y c o n s t i t u t e d t h e computer has t h e l o g i c a l and d i g i t a l
(9"
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components shown i n Figures HA and -3. A l l t h e s e components a r e
a v a i l a b l e . f o r i n t e r c o n n e c t i o n through a removable problem p r e p a t c h p a n e l and a l l connections a r e mLde by t h e fainiliar analog
p a t c h i n g method.
AtA(<
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For purposes of i l l u s t r a t i o n , t h e computer components have -&c:,Lt
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two g e n e r a l c a t e g o r i e s :
1)
l o g i c a l o p e r a t i o n components,
2)
d i g i t a l word components.
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c
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The l.ogical u n i t s permit nechanizarion of 3 o l e a n a l g e b r a
f u n c t i o n s , and t h e i r i n s e r t io::
accomplished"by- coqz-:atom
analog compi:dr
ani! D/A swlzches.
i m p s Le
Comparators serve
t o i n t r o d u c e analog e v e n t s i n t o t h e l o g i c c c x p u t e r , Lhe s t a t e
change
of t h e i r a i g l t a l output marking t h e coincidence of a n a l o g
cQmputer v a r i a b l e s .
The d i g i t a l l y - c o n t r o l l e d a n a l o g switches ,
o r D/A.switches, permit t h e i n t r o d u c t i o n of l o g i c a l events i n t o
c o n t r o l loops of t h e analog program by c o n t r o l l i n g t h e i n p u t s t o
operational amplifiers.
The b a s i c Logic elements of t h e DLS,
16
shown i n Figure A';,a r e s e l f - e x p l a n a t o r y .
The pre-organized
l o g i c elements shown i n t h e same f i g u r e are elements t h a t would
r e q u i r e s i z e a b l e s e c t i o n s of b a s i c l o g i c t o mechanize.
Therefore,
b a s i c l o g i c i s prepackaged t o perform t h e s e more d i f f i c u i t
f u n c t i o n s by simple i n p u t and output connections.
This g r e a t l y
s i m p l i f i e s t h e programming, b e t t e r u t i l i z e s t h e a v a i l a b l e p a t c h
p a n e l h o l e s and i n c r e a s e s t h e c o s t .
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The d i g i t a l word componentshconsist of t h e u s u a l m u l t i p l e x e r
( M P X ) , a n a l o g - t o - d i g i t a l c o n v e r t e r (ADC) and d i g i t a l - t o - a n a l o g
c o n v e r t e r (DAC) u n i t s similar t o t h o s e r e a d i l y a v a i l a b l e on t h e
commercial market.
These u n i t s provide t h e c a p a b i l i t y of
t r a n s l a t i n g analog v a l u e s i n t o d i g i t a l numbers and v i c e v e r s a .
The d i g i t a l numbers s o generated c a n be s t o r e d , o u r i u t e d o r
o t h e r w i s e o p e r a t e d on by use of t h e s t o r a g e and readout elements
shown i n Figure
A&.
The memory elements (SM8, e t c . ) a r e a c o u s t i c
d e l a y l i n e s c u t t o v a r i o u s m u l t i p l e s of t h e 16 b i t d l g i t a l words
used i n t h e DLS.
The memory b u f f e r (NB) i s a n element f o r
temporary h o l d i n g of d i g i t a l words f o r i n s e r t i o n inCo memory l i n e s
a t t h e appropriate interval.
The papzr t a p e p i x c n and r e z d e r permit
f a s t i n p u t and output of DLS l o g i c s t a t e s o r d i g i t a l numbers.
The DLS h a s been a p p l i e d t o a v a r i e t y of problems a t t h e
Ames Research Center and promise f o r f u t u r e a p 2 l i c a t i o n s seems
unlimited.
P a r t i c u l a r l y g r a t i f y i n g h a s been t h e new areas of
problem work a v a i l a b l e t o t h e s i m u l a t i o n computers when
i n t e r c o n n e c t e d w i t h t h e DLS.
These a r e a s include:
1) Data a p p l i c a t i o n s
2)
3)
a.
Data r e d u c t i o n
b.
Data work-up
c.
Data readout
Simulation Applications
a.
Simulation of l o g i c a l c o n t r o l systems
b.
Simulation of t r a n s p o r t delays
c.
Simulation d i s p l z y g e n e r a t i o n
Computer Control A p p l i c a t i o n s
a.
Analog computer c o n t r o l
b.
Linkage system c o n t r o l
To i l l u s t r a t e t h e f u t u r e p o t e n t i a l and p r e s e n t s u c c e s s of
t h i s machine, s e v e r a l problems t h a t have beeil r u n w i l l be d i s c u s s e d .
Figure
t i 9
i l l u s t r a t e s a method of computing average h e a r t
r a t e from e l e c t r o c a r d i o g r a p h (ECZ) s i g n a l s t h a t have been s t o r e d
on magnetic t a p e .
The a c t u a l problem requirsd t h e r z d u c t i o n of
c o n t i n u o u s ECG d a t a from t w o s u b j e c t s snclosed i n a s m a l l c a p s u l e
f o r seven days.
If one assumes one h e a r t b e a t p e r second, t h e
d a t a tapes contained 1.8 m i l l i o n h e a r t b e a t s of t h e two s u b j e c t s .
The requirements of t h e biotechnology department w a s a time
average of h e a r t r a t e over a f i v e ( 5 ) mlnute p e r i o d ; t h i s t o
be computed c o n t i n u o u s l y f o r t h e seven ( 7 ) days a c c u n u l a t i o n
I>-
of t e s t d a t a .
7 2
P
CijULI2 * >
,t
311uw3
h e a r t r a t e from t h i s ECG dzca.
the b a s i c
y-L
nc
u I5
-c
A-L
- .lr
Lu
nnm
L
uLq~te
A c o m ? z a t o r d e t s c c s tl:e
peaks
by s e t t i n g t h e r e f e r e n c e l e v e l t o i n t e r s e c t t h e main p e d < only.
The output of che comparator i s accumulated i n c o u n t e r f o r f i v e
minutes t h e n t h e c o n t e n t s o f counter a r e p r i n t e d o u t , t h e c o u n t e r
c l e a r e d and begins counting again.
However, playback i n r e a l
time i s v e r y uneconomical, and playback a t 16 h c h e s per second
(I PS) w a s s e l e c t e d .
The box of Figure B shows t h e r e l a t i v e
r e c o r d t o playback t i m i n g obtained by simply i n c r e a s i n g t h e
playback t a p e speeds.
The t a p e playback of i6 -i?S from a r e c c - d i n g
speed of 1 7 / 8 I P S lowers t h e running time of t h e playback
computation t o 10.5 h r s .
The l o g i c components and comparators
p r e s e n t no d i f f i c u l t y a t t h i s speed, as t h e y s t i l l a r e orCsrs of
magnitude f a s t e r t h a n playback events ( i . e . ,
i n 10Jksec.).
comparators sv;ritch
Of concern a t t h i s playback r a t e i s t h e s;?eed o i
t h e p r i n t o u t mechanism,wnich a t t h i s time w a s a n HP.560 p r i n t e r .
T h i s problem i s handled by devoting one r e g i s t e r as a h o l d i n g and
p r i n t o u t r e g i s t e r while a n o t h e r r e g i s t e r accumulates t h e immediately
following counts.
For two s u b j e c t s t h e p r i n t e r i s permi-Lted n i n e
(9) seconds p e r p r i n t o u t ; a very s a t i s f a c t o r y s a f e t y margin f o r
s t a n d a r d p r i n t e r s such as t h e H-P
&&).
i,Z
The method of Figure 3 has t h e disadvantage of r e a d i l y
responding t o n o i s e s p i k e s and secondary h e a r t z e t i o n s such as
systoles.
To a i d i n d i s c r i a i n a t i n g a g a i n s t t h e s z extraneous
I-
s i g n a l s , a "window" g e n e r a t o r snown i n F i g a r e - 9 z ~ ~ a j :
nechanized
- - - - ---
.
.
.
.
3
c
I
I
',
u s i n g a d i f f e r e n t i a t o r , two f l i p - f l o p s and a down-counter.
Figure { # i l l u s t r a t e s
the f i n a l c i r c u i t configuration.
Using
t i m i n g marks from t h e d a t a , i n s t e a d o f from machize-generated
t i m i n g , t h e system can be operated a t any t a p e speed, provided
t h e "window" i s a d j u s t e d t o f i t t h e p k y b a c k p u l s e i n t e r v a l .
S c a l i n g of t h e output r e a d i n g s f o r d i r e c t p r i n t o u t of average
h e a r t r a t e i s acccomplished by t n e double counting e f f e c t of the
.
l e a d i n g e d g e - t r a i l i n g e d g e - d i f f e r e n c i a t o r a c e i o n and d i v i s i o n by
10 on t h e BCD c o u n t e r by s h i f t i n g t h e decimal p o i n t , r e s u l t i n g
i n t h e ' r e q u i r e d d i v i s i o n by f i v e (5).
A summary of n e c e s s a r y
l o g i c elements snows:
19 flip-flops
90 AND g a t e s
15 decades down-counting
8 decades up-counting
8 decades down-counting (used as holding r e g i s t e r s ) .
T o t a l running time, i n c l u d i n g t a p e h a n d l i n g , w a s two days.
A somewhat a l l i e d technique of p r o c e s s i n g d a t a by l e v e l
s e l e c t i o n and accumuLation of r e s u l t a n t counts has been e x p l o i t e d
by M r . W.D.
Cameron of t h e Ames Research Center s t a f f , which has
been r e p o r t e d s e p a r a t e l y i n d e t a i l .
&
An example of t h e v e r s i t i l i t y of t h e DLS i n f l i g h t s i m u l a t i o n
problems w a s p a r t i c u l a r l y apparent i n i t s a p p l i c a t i o n t o a t r a c k i n g
&;H,u.L
task
simulator-
L.. FIG '6
I n t h i s i w e s t i g a t i o n , t h e s t a t i s t i c s of t r a c k i n g
e r r o r s o f p i l o t s w i t h randomly v a r i a b l e i n i t i a l r o t a t i o n a l
d,&d*-
a c c e l e r a t i o n s of t h e v e h i c l e ~
2 3
undzr
study.
F+,xe
<+
degree of p s r t i c i p a z l o n of ';he DLS i n t h 2 s l i m l a t i o s .
1) COC-LYOLS a c a l o g eom;?xter m d e r p i l o t COX.^^,
->
shows t h e
T k DLS:
2)
Generates c o n t r o l p u l s e s f s r i m e r t i o n i n t o analog
computed dyr,z,r;?ics,
3)
Accumulates c o n t r o l 2u;ses
4)
Randomly s e l z c t s +,
f;::.
- i - z ~ consu.:: :ion compctation,
-
7
- zero r e f e r z n c e i n d e p e n d m t l y f o r t h r e e
(3) integrazor I C poteatiometers,
5)
G e x r a t e s t h e o s c i l l o s c o p e d i s p l a y p a t t e r n fror. analog
conputer o u t p u t s ,
6)
Records a l l d a t a output channels on punched paper t a p e .
cy.:
I n t h e o p e r a t i o n of t h e sirnulat!--m, t h e y i l o t s c e e r s t h e
d i s p l a y by u s i n g a s t z z d a r d bang-bang c o n t r o i l e r .
Upon
s u p e r p o s i t i o n of t h e t a r g e t Cots, t h e p i l o t actclstes t h e IrRead"
switchy
,
t
. f
Llh..b!<.tr
II
~4;~1~,=~~..~;12.21~,~.~~~~"
is the
basic c o n t r o l input
I
t o t h e DLS,
pi-. 1
;ne
f o l l o w i n g sequence t h e n occurs:
1) DLS p l a c e s analog i n hold,
2)
DLS r e a d s out seven (7) end-point q u a n t i t i e s by a c t u a t i n g
t h e m u l t i p l e x e r , ADC, paper t z p e punch recordiiig system,
3)
DLS p l a c e s analog i n I C ,
4)
DLS sets t h r e e new I C c o n d i t i o n s ,
5)
DLS w a i t s 0.5 seconds f o r I C c h a r g i n t t i m e ,
6)
DLS p l a c e s ar,alog i n o p e r a t e and
a.
generates display t o p i l o t
b.
generates c o n t r o l pulses
c.
accumulates c o n t r o l p u l s e s .
O f p a r t i c u l a r i n t e r e s t i 2 t h i s problem was t h e erqloym~nt
of t h e h i g h speed paper t a p e punch 1/0 u n i t i n s t e a d of t h e
s t a n d a r d AEIOS t y p e w r l c e r readout.
The readout of seven (7)
q u a n t i t i e s on t h e mlCS took a minirrxm of 2 1 seconds and t h e
.
/:
.
a d d i t i o n of addlzicn-!.
readout p o i n t s was e s s e n t i a l l y l i m i t e d
by t h e slow ADIOS speed.
Since hundrsds of such runs a r e
n e c e s s a r y , t h i s w a i t i n g p e r i o d zmounts t o hours of i d l e computer
and p i l o t time.
The DLS conversion and ?ur,c'r, equipriient w a s
employed a s shoim in Figure
I7
_ . The cor:.rerted v s l c r s a r e t r z n s f e r r e d
-
I
i n c h a r a c t e r g r o q s of f o u r b i t s t o t h e pumh d r i v e r s iii p a r a l l e l .
3
It t a k e s & l i n e s of punching t o r e p r e s e n t a 1 2 b i t b i n a r y word
[w-,P
4
44
pLz3 a l i n e f o r , s l g n .
A f i f t h (5) l i n e i s used f o r indexing.
The maximum speed of t h e readout i s , t h e r e f o r e , 22 bizlary words
p e r second as t h e punch h a s a 110 c h a r a c t e r p e r s2cor.d ;?unching
rate.
The ADC, a t 4 , C J O words/sec.,
i s no l i m i t a t i o n whscever
t o t h e output r a t e .
The time r e q u i r e d f o r r e c o r d i n g t h e n e c e s s a r y out2uc d a t a ,
p l a c i n g new IC's on t h e analog, r e s e t t i n g and p i t t i n g i n t o o p e r a t e
i s 0.8 seconds as compared t o 2 1 seconds of t h e AZiOS -- a
s u b s t a n t i a l improvement.
I n f a c t , f o r a human o p z r a t s d Levice
l i k e t h i s i t i s t o o f a s t and some a d d i t i o n a l wai-sicg time f o r
human recovery has t o be introduced.
The i n t e r v a l of 0.8 seconds
i s j u s t t o o s h o r t , b e i n g about long enough t o push t h e r e a d b u t t o n
& &.-)-,j* C? T L !
;; c,(+*r,>
and b l i n k your eyes b e f o r e the-nexk r u n has began.
f.-
Afcer a s e r i e s of r u n s a r e completed, t h e h t a p e s a r e t a k e n
t o t h e daca p r o c e s s i n g l a b o r a t o r y f o r immediate p r o c e s s i n g and
s t o r a g e on magnetic t a p e .
When s u f f i c i e n t r u n s f o r s t a t i s t i c a l
5 (-i%
e v a l u a t i o n are completed, t h e s L a n d a r d i d h a p r o c e s s o r s can compute
Cri-
any d e s i r e d f u n c t i o n s a d otherwise s e r v i c e t h e d a t a .
This method
o f d a t a t a k i n g r e p r e s e n t s a major s a v i n g i n tzch:-iicsi manpower i n
r u n n i n g c h i s t y p e of program, and makes a ; ; a I o g - c x ~ 3 t e d r e s u l t s
. .. .
i n s t a n t l y a v a i l a b l e t o powerful d i g i t a l computer a n a l y s i s .
The DLS p o r t i o n o f ' t h e problem uses t h e f o l l o w i n g c o ~ p o n 2 r ; t s :
~:2
Flip-flops
[c3 AhQ gazes
30
D/A switches
C GC up-cocnters
PC down-counters
3 Shift registers
/" Comparators
3 M P X , ADC, PTP
a
The r e s u l - s
UL
- h i s program have been m o s t g r a t f Y .ng
.
Tfie primary
t h e s i m u l a t i o n of t r a n s p o r t delay.
The f i r s t d e l a y simu;a;ion
has
been implemented a t t h e Center and some d i s c u s s i m of t h e p r e l i m i n a r y
e x p e r i e n c e using d i g i t a l s t o r a g e methods seems a p p r o p r i a t e .
The b a s i c problem involved t h e s i m u l a t i o n of a j e t engine
1
8
c o n t r o l system a t s u p e r s o n i c speeds, shown i n Figure G. The
t r a n s p o r t d e l a y s of t h e shock d i s t u r b a n c e s a t t h e i n l e t t o t h e
e x i t w e r e mechanized by u s i n g a v a i l a b l e DLS components of Figure)
JO
!!
h\L,\, 7";tL(
t, '!) dA!?p
4 S and $3. The r e q u i r e d d e l a y s w e r e , z,o-shswn.-in--Flgu~~~G;
2.5
&.<,I
1 . 6 7 and 0.714 seconds r e s p e c t i v e l y .
.e-'
A v a i l a b l e d e l a y l i n e s are
256 (SM8), 64(SM6) and i6(SM4) words long.
Noting t h a t sampling
r a t e i s the r a t i o of l i n e l e n g t h to d e l a y r e q u i r e d , t h e c h a r t of
F i g u r e 6 shows t h e r e q u i r e d sampling p e r i o d s .
1 8
These sampling
f r e q u e n c i e s are, u n f o r t u n a t e l y , rinrelated ~ - - a r m o L L l c ~ l
and
i y because
t h e r e are t h r e e simultaneocs delay c h a i u x l s i n op<.:rtion but only
one ADC i n t h e analog realm, d a t a skewizg r e s l i l t s a 2 a c c u r a t e
sampling becomes very d i f f i c u l t t o achieve even i f a random
a c c e s s MpX and sample h o l d i n p u t s were a v a i l a b l e .
These l a t t e r
components were n o t a v a i l a b l e s o an a l t e r n a t e scheme of sampling
i n t h e d i g i t a l realm was devised.
9
I l l u s t r a t e d i n Figure v , t h e
method uses t h e maxinum up-dating r a t e of t h e MPX-ADC combination
i n t o t h r e e one-word memory b u f f e r s ( M B ) .
c,.*.l.:J
Each s i g n a l i s sampled
2.4
1,300 times/second and t h e MB c o n s t a n t l y s u p p l i e d with new d a t a .
The d i g i t a l sampling f o r t h e delay of each channel i s e f f e c t e d by
ANDing a "sample" s i g n a l w i t h the MB o u t p u t .
Simuitaneous with
i n p u t i n g t h e delay l i n e , t h e proper word must be t r z n s m i t t e d t o
t h e w a i t i n g DAC.
However, i f the proper word i s not i n &he o u t p u t
p o s i t i o n , t h e t r a n s f e r process m u s t be held up u n t i l t h e memory
c i r c u l a t e s t h e d e s i r e d word t o the o u t p u t p o s i t i o n .
This l e n g t h
of time v a r i e s depending on t h e memory access time.
I n t h e SM8,
t h e a c c e s s time i s 2 m i l l i s e c o n d s .
This 2 m i l l i s e c o n d s becomes
t h e maximum h o l d i n g time b e f o r e t h e sampler can e n t e r i n z x m a t i o n
i n t o memory,but on t h e average w i l l be s u b s t a n t i a l l y l e s s t h a n 2
milliseconds.
Notice, though, t h e u p d a t h g of MI3 concircles s o
t h a t when t h e a p p r o p r i a t e t r a n s f e r time does occur, k i e r information
has been p u t i n t o t h e MB by t h e ADC, MPX combination. --;.'The
*<
(kc8 kJ.cr.-cL w tfeLQ
.
I
A*/e f f e c t , , i s always t o delay t-he-cc;-p&-zd
somewhat. I C i s
b e l i e v e d t h a t t h e e r r o r s introduced by t h e s e delays a r e small
compared t o o t h e r system i n a c c u r a c i e s such a s t h e ADC, sampling,
etc.
However, problems of programming t r a n s p o r t delays on d i g i t a l
equipment have been g l c s s e d over aria c o n s i d e r a b l e i n v e s t i g a t i o n i s
needed t o f i n d a maximum accuracy, minimum componect program f o r
m u l t i p l e channel d e l a y s .
.- .
... -
.
Such e f f o r t s a r e under way a t t h i s Center.
.
(r
&,fJ
‘.:,, ’
‘i 4
1 ,
1 ‘4
p
F u r t h e r , a g r c ~ t :2zc-’l CC improvement i n t h e 2rogramming methods
f o r d i g i t a l word components a r e r e q u i r e d .
A t present, a great
d e a l of e f f o r t ’ i s expended t o decipher t h e manuzacturers c r y p t i c
(Fa‘.
i n s t r u c t i o n manuals which a r e ‘ devoid of t h e most important item,
a timing diagram.
These p r o b i e r s a r e t o be ex2ected when
s t e p p i n g t o a new a r e a , *q2&
1; <.sa&
%L.-
4-
:, rL
s:
;2
&
r z d experizince e-;L mske
l a t e r machines much more manageAle i n this r e s p e c t .
.
CONCLUSION
Two major h y b r i d computer systems have been d e s c r i b e d
b r i e f l y , em?hasizir,g t h o s e f e a t u r e s which make them extremely
p o t e n t i n the g e c e r a l fLeld of r e s e a r c h f l i g h t s i m u l a t o r s .
,
The Ames Linkage System, while followixg t h e f a m l l l a r
s
"slender coupling" d e s i g n concept, has s u c c e s s f i l - y connected
two remote computers t o g e t h e r i n a s i m u l a t i o n a T p X c a t i o n .
This,
combined w i t h e x t e n s i v e remote readorris and c o n t r o l and t h e unique
Data Acceptance Routine, makes e l a b o r a t e space ve;iicLe f i i g h t
s i m u l a t i o n p o s s i b l e a t the Center.
The use of t h e Linkag. i n
t h e r e e n t r y phase has been d i s c u s s e d .
The D i g i t a l Logic Simulator on she o t h e r hand r e p r e s l x s a
new computer concept a t t h i s Center.
'The machine h a s f o u n d
widespread u s e i n s i m u l a t i o n l a b o r a t o r y due b a s i c a l l y t o I t s
g e n e r a l purpose d e s i g n .
The a p p l i c a t i o n s d i s c u s s e d have been
s e l e c t e d t o h i g h l i g h t the u n i p e c a p a b i l i t i e s of t h i s t y p e 'of
equipment i n h y b r i d c o m p t a t i o n .
.
1. Anon. : EM-3 K u l t i p l e x e r TschnLzal Manual PBC 3014,
Packard B e l l Computer Company, 1905 Xrmhzost Ave.,
rLUD
,,
A----I--
N L ~ C L C D
9c
~
2
P 1 'c
4
,i r i L .
3n
h..-.--&
AU~UDL LU,
i n c 3
L ~ U L
2.
Anon. : M-2 MulEiverter Technicel PIaxu~: PEC 3020,
Packard B e l l Compter Conpany, 1935 Arclacost Ave. ,
Los Angeles 25, Calif. November 7 , 1962
3.
Anon.:
DA6 Digital-to-Analog Converter Technical
Manual PBC 3G03, Packard B e l l Computer Company,
1905 Armacost Ave. , Los Angeles 25, C a l i f . September
1, 1961
4.
Fogarty, L.E., Howe, R.N. : ? l i g h t Sirnulation of O-+i:-ai
and Reentry V z h i c l e s , P a r t I1
A Mocifiecl F l i g h t &...::.
Axis System f o r Solving t h e S i x Degree-of-Freedom F l i g h t
Equations. ASD Technical Report 61-171 (11), October 1961
5.
I b i d . p . 25
6.
Cameron, W.D.:
DeterminaZizA of P r o b a b i l i t y D L s t r l b u t l o n s
Using Hybrid Conputer Techniques. Proce?.riilg of t h e
I n t e r n a t i o n a l Symposium of Analog and D i g l c a l Techniques
Applied t o Aeronautics. Se2tember 9-12, 1963
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