Epson PX-8 - Page 44

REV.-A
2.2.4 Backup Circuit
The following elements are backed up by the battery voltage (VB) while power is off in order to
protect data in the RAMs and maintain a clock feature, etc.
Table 2-3 Battery Protected Component
Location Element name Function
4D ~ 7D
RAM Main RAM (dynamic)
4E
~ 7E
9C
~ 11 C V-RAM
LCD display RAM (static)
2E
4-bit sub-CPU Power control, keyboard scanning
3D Gate Backup line control
3E Gate Power-on signal gate
4C,6A
Gate array Interrupt and clock control, etc.
*1 D a-bit AD converter
Battery voltage detection and temperature change detec-
tion (for RAM refresh rate determination), etc.
* The
operating voltage is supplied for a ms every 10 seconds.
The backup
circuit is
shown in Fig. 2-13. As
can be seen, the circuit is
normally backed up from
the VB line via the transis-
tor Q23, regardless of
whether the computer is
operating
or not. It is
backed up
from the auxi-
liary
battery when low
voltage is detected.
For details
of the circuit
20K
Rt43
B970
-IRS
SW5
B970-IRS
'---_'""""""'IIVIr----,RDZ
4MB
016 MAISl
WK
Backup line
operations, refer to the From auxiliary battery
descriptions on the power
on/off circuit.
12
70508
P42
40K
VB
Fig. 2-13 Backup Circuit
2-20
7508
P70