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T H E O R Y O F O P E R A T I O N S
T h e C P - A f r o n t p a n e l a s s e m b l y p r o v i d e s m a c h i n e s t a t u s
i n d i c a t o r s , u s e r c o n t r o l l e d s w i t c h e s , a n d c o n t r o l
f u n c t i o n s to t h e IMSAI
c o m m u n i c a t e s w i t h the M P U - A m i c r o p r o c e s s o r a n d o t h e r
b o a r d s t h r o u g h t h e 8080 b a c k p l a n e and, a d d i t i o n a l l y ,
c o n n e c t s
(via 16 c o n d u c t o r f l a t cable)
d i r e c t i o n a l d a t a bu s o f the 8 0 8 0 m i c r o p r o c e s s o r .
T h e C P - A p a n e l u s e s 44 L i g h t E m i t t i n g D i o d e s as f r o n t
p a n e l i n d i c a t o r s .
c o r r e s p o n d to s i g n a l l e v e l s o n t he I M S A I 8 0 8 0 b a c k
p l a n e , a n d are d r i v e n d i r e c t l y f r o m t h e b u s w i t h n o
i n t e r v e n i n g logic.
16 A d d r e s s Bus L ED' s ,
I N T E R R U P T E N A B L E D LED,
T h e
8080 m i c r o p r o c e s s o r c h i p s b i - d i r e c t i o n a l d a t a bu s
l e v e l s
( p r o v i d e d by a 1 6 - c o n d u c t o r cable)
o n the D A T A bus
s c h o t t k y h e x i n v e r t e r )
b i - d i r e c t i o n a l b u s is t h e 8212 8 b i t l a t c h u s e d t o d r i v e
t h e P R O G R A M M E D O U T P U T i n d i c a t o r s .
d r i v e n d i r e c t l y fro m t h e r u n / s t o p f l i p - f l o p
t h e C P - A B o a r d .
T h e 16 A D D R E S S - P R O G R A M M E D I N P U T a n d A D D R E S S - D A T A s w i t c h e s
a l l o w t h e o p e r a t o r to p l a c e d e s i r e d v a l u e
a d d r e s s e s )
on t h e 8 0 8 0 ' s b i - d i r e c t i o n a l bus.
As
s h o w n on t h e s c h e m a t i c ,
(open c o l l e c t o r )
c o n f i g u r a t i o n .
P u l l u p r e s i s t o r s on t h e M P U B o a r d e n s u r e t h a t t h e b u s
l e v e l s a r e a l l h i g h u n l e s s a n y i n v e r t e r o n a ny o n e of
t h e b u s lines g o e s low.
(this c o n d i t i o n w i l l b e d i s c u s s e d sho r t l y )
s w i t c h c a n b e u s e d t o p u t e i t h e r a h i g h o r low v a l u e
o n t h a t l i n e .
T h e f u n c t i o n s w i t c h e s p r o v i d e t h e o p e r a t o r w i t h d i r e c t
c o n t r o l o f t h e m i c r o p r o c e s s o r .
c o n t r o l s
t h e X - R E A D Y l i n e v i a t h e R U N / S T O P f l i p - f l o p .
8080 o p e r a t o r .
M a n y of t h e s e i n d i c a t o r s d i r e c t l y
I n d i c a t o r s
in t h i s g r o u p a re t h e
t h e 8 S T A T U S b y t e L E D ' s , t h e
the W A I T LED,
i n d i c a t o r s v i a t he
s e c t i o n s .
t h e s e s w i t c h e s c o n n e c t 7405
i n v e r t e r s t o t h e b u s in a w i r e d - A N D
Thus,
if a n i n v e r t e r g o e s low,
CP-A
Theory of Operations
Revision l
T h e C P - A b o a r d
to t h e b i
a n d t h e H O L D LED.
a r e d i s p l a y e d
74LS04
(low p o w e r
A l s o d r i v e n f r o m t he
T h e R U N i n d i c a t o r is
(74107)
(program, data,
the a d d r e s s
T h e R U N / S T O P s w i t c h
on
4 - 3
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