Epson PX-8 Technical Manual page 30

REV.-A
2.2.1 Power On/Off Control
The power circuits are controlled by the 4-bit CPU 7508 which operates under a control program
stored in a mask ROM built in it. If the CPU runs away due to some reason (battery power exhaus-
tion for example), therefore, the power supplies are completely out of control. If this occurs, the
AC adaptor should be connected to charge the batteries and then SW5 should be pressed to reset
the CPU 7508.
2.2.1.1 Power On
The computer is turned on by either of the following:
(1) Setting the POWER switch ON
Setting the POWER switch ON causes pin 23 of CPU 7508 (INTO) to go high (see Fig. 2-4)
which interrupts the control program for turning power on.
(2) Programmed power on
Power is automatically turned on regardless of the POWER switch setting when the time spe-
cified softwarewise with a "WAKE" command coincides with that of the clock built in CPU
7508.
2.2.1.2 Power Off
Power is turned off by one of the following:
(1) POWER switch OFF
Turning the POWER switch OFF causes pin 23 of the 7508 CPU (INTO) to go low (see Fig.
2-4), interrupting the control program for turning power off.
(2) Low voltage detection
When a low VB line voltage is detected. The 7508 CPU interrupts the main CPU and current
processing to be terminated at an appropriate point. At the same time, "CHARGE BATTERY"
message display on the LCD screen for 30 seconds. The 7508 CPU then automatically turns
power off if the POWER switch is at the ON position.
(3) Automatic (programmed) power off
The computer can be turned off by a software automatic power-off feature which uses the
7508 CPU's built in clock. This feature automatically turns power off when no I/O unit is used
for a certain period of time even though the computer is in the key entry mode. Power off tim-
ing as follows:
• Default: 10 minutes
• Specified: 1 to 255 minutes (specified by using the CONFIG command)
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