Bally 5000 Plus, Manual

Page: 95 / 388

3 . MPU BOARD
C i r cu i t D e s c r i p t i on ( con t ' d )
E P ROM
E a c h e r a sab l e , p r og r ammab l e memo r y
( E P ROM ) func t i ons w i t h ano t h e r a s a
pa i r I n t he boa r d pos i t i ons o f U 1 2
& U 1 5 a n d U 1 8 & U20 . E a c h pa i r may
cons i s t o f 2-256K E P ROMs w i t h 64K
by t e s ( 32K wo r d s ) o r 2-5 1 2K E P ROMs
w i t h 1 28K b y t e s ( 64K wo r ds ) .
I n f o r ma t i on can on l y be r e a d f r om
t he E P ROMs .
So f t wa r e c h i p
U 1 8 , and U 20 .
t h i s S e c t i on .
se l ec t s U 1 2 , U 1 5 ,
See C h i p Se l e c t
I n
U 1 0 p i n 1 6 sends t he ROM c h i p
se l ec t ( ROM 1 CS ) s i gna l t o U 1 2 p i n
20 and U 1 5 p i n 20 . U 1 0 p i n 1 7
sends t he ROM 2 c h i p
se l ec t
( ROM2CS ) s i gna l t o U 1 8 p i n 20
and
U20 p i n 2 0 .
T h e s i ze o f t he E P ROM and t he
J umpe r se l ec t i on o f J 1 a n d J 6 a t
U 1 0 de t e r m i ne t he a d d r ess bounda r y
o f e a c h E P ROM . T h e U 1 0 J umpe r
se l ec t i ons a r e a s f o l l ows :
256K ( 32K b y t es )
J 1 J 6
U 1 2 & U 1 5
U 1 8 & U20
5 1 2K ( 64K b y t e s )
J 1 J 6
o
0 U 1 2 & U 1 5
o
0 U 1 8 & U 2 0
Read l owe r d a t a b y t es
To r e a d f r om t h e l owe r d a t a b y t es
ove r t he l ower d a t a l i ne s ( DO-D7 ) ,
U 1 2 f r om t he pa i r , U 1 2 & U 1 5 , and
U 1 8 f r om t he pa i r , U 1 8 & U20 , need
( 1 ) an odd a d d r ess ( 2 ) a c h i p
se l ec t s l gn
�
and ( 3 ) an ou t pu t
enab l e l ow ( OE l ) s i gna l .
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