Bally 5000 Plus, Manual

Page: 101 / 388

3 . MPU BOARD
C i r cu i t Descr i p t i on ( cont ' d )
P I A
The p a r a l l e l I n t e r f ace a d a p t e r
( P I A ) I n t e r f a ce s I t s p a r a l l e l I /O
por t s w i t h t he Message Cen t e r
d i sp l ay a n d mon i to r s t he b a t t e r y
cond i t i on .
So f t wa r e c h i p se l ec t s U 1 9 . See
Ch i p Se l ec t I n t h i s Sec t i on .
U 1 0 p i n 1 9 sends t he l oc a l I /O
s i gna l to U7 p i n 1 8 .
U7 p i n 5 sends t he c h i p se l ec t P I A
2
( CSP I A2 ) s i gn a l s i mu l t aneous l y
t o :
( 1 ) U 1 0 1 p i n 1 6 .
Then , U l 0 l p i n 1 7 sends a VPA
s i gn a l to Ul p i n 2 1 .
Ul p i n
1 9 send a VMA s i gna l to U 2 1
p i n 1 3
.
U 2 1 I nver t s t he
s i gna l . U 2 1 p i n 1 2 send a VMA
s i gna l
t o t he P I A ( U 1 9 p i n
25 ) .
( 2 ) U 1 9 p i n 2 3 .
U 1 p i n 2 0 sends t he enab l e ( E )
c l ock s i gna l to U 1 9 p i n 2 5 .
When U 1 9 h a s r e c e i ved t he 3
s i gna l s a t p i n 2 1 , p i n 2 4 , and p i n
25 . U 1 9 I s r e a d y for commun i c a t i on .
U 1 9 commun i ca t es t h r ough t he b i ­
d i r e c t i ona l d a t a bus l i ne s , 07 ( p i n
26 ) t h rough DO ( p i n 3 3 ) .
So f t wa r e
addr esses U 1 9 t h rough A l ( p i n 36 )
and A2 ( p i n 35 ) .
U 1 p i n 9 sends a R/W s i gna l t o U 1 9
p i n 2 1 .
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NOT E S