Advertisement
2-2. Circult description
4) RAM Read/write circult
HM5264
pPD75217
Data bus
i
po-07 K
DOYA7-D7/A0
Address bu
ADAI2
P32
40
AB-AIL
WE
We
os E
tsi
Fig. 2-2
Since the 8-bit data bus of the pPD75217 shares the same lines
with the 8-bit address bus of the HM6264, selection of the RAM
chip by the pPD75217 causes the HC973 to latch the 8-bit
address when P32 of uPD75217 is inputted.
DOK?
~DIIA2
HC978
output
Ta
=
wR
H
RAM data read timing
2) Battery Circuit
o
os
.
v0.00 —D+
De
vecisvi
ama
voo isv
a0
cr
—-
: Battery recharge current
---+ : Battery discharge circuit
Fig. 2-3
3) P-OFF Circuit
Power SW
Torr eweon
Fig. 2-4
At power on
When P-ON voltage reaches 16V, the current flows through the
zener diode (MTZ16B) so that the level at point @ goes high.
'The eve} of P-OFF rises as VCC increases. As a result, the P-
OFF signal changes from low to high level.
At power off
When the power is turned off, the P-ON voltage drops under 15V
causing the zener diode to stop current flow, which causes
potential at point @ to drop.
Power ON
Powe: OFF
sav
Pon
/
\
as
tov
rom @
/
\ eno
tv
Pore
Se
~
8y
Reset
GND
Fig. 2-5
4) Key and switch
so~-S11
Key scan signal
POS, P1i~P13
Key return signal
vo
:
Power switch
P-ON
Made switch
P3ok
Mode switch
Return signat
Advertisement
