Bally 5000 Plus, Manual

Page: 81 / 388

3 . MPU BOARD
C i rcu i t Descr i p t i on ( cont ' d )
The wa t ch dog t i me r c i r cu i t
cons t a n t l y mon i t o r s t he E PROMs for
s i gna l s
sen t wh i ch s how t he
m i c roprocessor I s f un c t i on i ng
p roper l y . T h i s
c i r cu i t I s
compr i sed o f t wo 1 4 s t age , b i na r y
r i pp l e coun t e r s cascaded ( U47 and
U38 ) .
Sof twa r e c h i p se l ec t s U47 and U 38 .
See C h 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 .
r e s e t
1 1 and
T h i s
U7 p i n 7 sends wa t c h dog
( WDRST ) s i gna l to U 38 p i n
U47 p i n 1 1 a t t he same t i me .
s i gna l
r e se t s t he wa t c h dog
beg i ns ano t h e r 65ms coun t .
and
U47 p i n 1 0 cons t an t l y rece i ves t he
8 MHz c l ock s i gna l wh i ch y i e l ds a
65 ms t i me out .
W i t hou t a WDRST s i gna l , t he coun t e r
I nc r emen t s t o 2 t o t he 1 9t h powe r
( 524 , 288 ) a n d sends t he wa t ch dog
( WDG ) s i gna l to t he r e s e t c i r cu i t
wh i c h r e se t s t he 68000 m i c r o­
pr ocessor . T h e L E D s f l as h eve r y 65
ms .
WATCHDOG C I RCU I T
U 21
1 4 H C 0 5
S I P S
1 0 K
C L K O U T
8h1H,
S I P S
l O K ( 3 )
U 2 1
NOT ES
W O R ST
J I 5 14 H C 0 5
F i g . 3-7
3-24