C i r cu i t Descr i pt i on ( cont ' d )
Rea l T i me C l ocl<
The
r ea l t i me c l ocl< c i r cu i t I<eeps
ac t ua l t i me .
Be i ng compa t i b l e w i t h
t he 68000 m i c r op r ocesso r ,
sof t wa r e
c a n r a ndom l y add r ess I t f o r a t i me
read i ng and se t t i ng . T he r e a l t i me
c l ocl< I s ba t t e r y b a cl<ed .
T h e c l ocl<
( U 30 ) I s used as a 6800 dev i ce .
Sof t wa r e c h i p se l e c t s U 3 0 .
See
Ch i p Se l e c t I n t h i s S e c t i on .
U 1 0
p i n 1 9 sends
t he
l oca l
I /O
s i gna l
t o
U7
p i n 1 8 .
U7
p i n 3 sends a r e a l
t i me
c l ocl<
enab l e ch i p se l e c t
( RTC )
s i gna l
s i mu l t aneous l y t o :
( 1 ) U 1 0 1
p i n 2 3 .
Then , U 1 0 1 p i n 1 7 sends a VPA
s i gna l to t he U1 p i n 2 1 .
U 1
p i n 1 9 sends a VMA s i gna l
t o
U66 p i n 1 2 .
( 2 ) U66 p i n 1 3 .
W i t h bot h s i gna l s comb i ned a t U66 ,
p i n 1 1 sends an ac t i ve LOW
s i gna l
to U66 p i n 2 .
U 1 p i n 20 sends
t he
enab l e
( E )
c l ocl<
s i gna l
t o U46 p i n 9 .
T h e
S i gna l
I s I nve r t ed w i t h an ou t pu t
a t
p i n 8 to U 6 6 p i n 9 . U66 p i n 8
sends t he s i gna l t o U66 p i n 1 .
U66 p i n 3 sends t he
c h i p se l ec t
S i gna l t o U 3 0 p i n 1 . So f twa r e can
now
commun i ca t e
( t r an s f e r
da t a )
w i t h
t he r e a l t i me
c l oc l<
t h rough
t he
b l -d l r e c t l ona l
d a t a bus ,
DO
( p i n
7)
t h r ough
D3
( p i n
4 ) .
So f t wa r e a d d r esses U30 t h r ough t he
addr ess
l i nes A 1 ( p i n 1 2 )
t h r ough
A4 ( p l n 9 ) .
U 1 p i n 9 sends a R /
W
S i g na l t o U30
p i n 3 .
3 . MPU BOARD
NOT E S
3-31
Summary of Contents for 5000 Plus
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