Bally 5000 Plus, Manual

Page: 91 / 388

3 . MPU
BOARD
C i r cu i t Descr i p t i on ( co n t ' d )
Read uppe r d a t a b y t es
To r e a d f r om t h e upper d a t a b y t es
over t he uppe r d a t a l i ne s ( 08-
0 1 5 ) , U 1 00 needs ( 1 ) an even
a d d r e ss ( 2 ) a c h i p se l ec t s i gna l
and ( 3 ) an ou t pu t enab l e h i g h ( OE H )
s i gna
I .
T h e O E H s i gna l beg i ns w i t h U 1 p i n 7
send i ng
t he U O S t o U 1 1 p i n 2 . U 1
p i n 9 sends t he R /W s i gna l t o be
buf f e r ed I n U48 .
U48 p i n 1 8 sends
R /W to U42 . U 4 2 p i n 8 sends t he
I nv e r t e d R /W ( R EAD ) s i gna l t o U 1 1
p i n 1 . The UOS a n d R EAD s i gn a l s a r e
g a t e d t h r ough U 1 1 .
U 1 1 p i n 3 sends O E H t o U 1 00 p i n 2 2 .
Read da t a wor ds
U 3 1 and U 1 00 ope r a t e a s a pa i r . To
r ea d d a t a wo r d s over t he d a t a l i ne s
( 00-0 1 5 ) , e a c h pa i r needs ( 1 ) e v e n
a d d r esses ( 2 ) c h i p se l ec t s i gna l s
and ( 3 ) t h e O E H a n d O E l s i gn a l s
s i mu l t a neous l y .
Open S a f e RAM k e y
So f t wa r e se l ec t s U36 .
U 1 0 p i n 1 9 sends I oca
I
1 10 s i gna
I
to U7 p i n 1 8 .
U7 p i n 8 sends S a f e RAM open
( SROP E N ) s i gna l t o U 36 p i n 1 .
On l y du r i ng s e r i a l s h i f t o f i nput s
o
a n d E , wh i c h I s b a s e d on t he 4
MHz c l ock a t U 36 p i n 2 , doe s U 36
p i n 7 send a l og i c lOW s i gna l t o
U 4 1 p i n 1 and U 4 1 p i n 1 3 . T h e S a f e
RAM key I s open .
3-34
NOT E S