Epson PX-8 - Page 76

REV.-A
2.4.2 CR2 Oscillator Circuit
The output of the 32.768 kHz crystal oscillator is used as the counting signal for the built-in clock
and as the D-RAM refreshing timing pulse. Thus, the oscillator circuit is always backed' up by the
battery (from the VB line) to ensure the 32.768 kHz clock signal to be supplied to IC 6A
(GAH40D), regardless whether power is on or off.
Fig. 2-51 is a
circuit diagram of the CR2 oscillator circuit.
C22
VB R136 R135
CR2
026
I C45
C23
ZD3
C46
4
32.768KHz
025
R36
VB
Pull up for RXO signal line on the expansion
interface.
L- ____ ~ IC 120 pin 14 (Power ON/OFF control)
Fig.2-51 CR2 Oscillator Circuit
The signal waveforms at various
points should be observed as
shown in Fig. 2-52.
* The 1 kHz output to the 7508
(pin 51 of GAH40D) is available
while power is off.
5V
GAH-400 (6A)
1
KC
To sub-CPU
7508
pin 40
5V
20\.15
3E
Pi~ 3 lfLilillliUl
30
Pi~
4
Il n D n 0 OJ
5V
Fig. 2-52
2-52