Bally 5000 Plus, Руководство пользователя

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C i r cu i t Des c r i p t I on ( con t ' d )
Safe RAM
E a c h Sa fe RAM f u n c t i ons w i t h
ano t he r a s a p a i r I n t he boa r d
pos i t i ons o f
U31
a n d
U 1 00 .
T h e
pa i r cons i s t s o f
1 6K
b y t es or
8K
wor ds . S a f e RAM s t o r e s bookkeep i ng
I n fo r m a t i on , some game
s t a t us
I n forma t i on , a n d keypad o p t i on
set t I ngs . I n forma t I on can be r ead
f r om o r wr i t t en t o t he S a f e RAM .
Safe RAM I s b a t t e r y b a cked t o
p r e vent memo r y l oss when powe r I s
r emoved . The m i c rop r ocessor wr i t es
t o t he S a f e RAM key ser i a l s h i f t
r eg i s t e r ( U 36 ) b e f o r e d a t a can be
w r i t t en t o S a f e R AM .
T h i s p r eve n t s
t he S a f e RAM f r om be i ng cor r up t ed .
So f t w a r e c h i p se l ec t s
U31
and
U 1 00 .
See
£hla
Se l e c t I n t he Sect i on .
U 1 0 p i n
2 1
sends S a f e RAM c h i p
se l e c t s i gna l
(�)
s i mu l t aneous l y
t o U 3 1 p i n 20 a n d U l 00 p i n
20 .
R e a d l owe r da t a b y t es
To read f r om t he l owe r d a t a b y t e s
ove r t h e l owe r d a t a l i nes ( 00-07 ) ,
U 3 1 needs ( 1 ) a n odd a d d r e s s ( 2 ) a
c h i p se l e c t s i gna l and
( 3 )
a n
ou t pu t e n a b l e l ow ( OE l ) s i gna l .
The OEl s i gna l beg i ns w i t h
U1 p i n 8
send i ng
t h e l O S t o U 1 1 p i n 5 . U l
p i n
9
sends t he R / W s i gna l to be
bu f f e r e d I n
U48 . U48
p i n
1 8
sends
R /W
t o
U42 . U42 p i n 8 sends t he
I nve r t ed R/W ( R EAD ) s i g na l t o
U 1 1
p i n
4 .
T he l O S and s I gn a l s
a r e g a t ed t h r ough U 1 1 .
U 1 1 p i n
6
sends O E l t o
U31
p i n
22 .
3 .
M P
U
BOARD
NOT E S
3-33