General; Power Supplies - Epson PX-8 Technical Manual

REV.-A
2.1 General
This chapter describes various functions of the main control board (called MAPLE board) which is
the center of this computer. The microcassette drive and option units are described in Chapter 3.
The MAPLE board uses a diversity of fully customized ICs (referred to as gate arrays throughout
this manual), masked ROMs, and other chip elements (resistor, capacitor, transistor, and diode
chips) which simplify component mounting. As many CMOS elements as possible have been
used in order to lower power consumption. In addition, the computer provides the following fea-
tures in order to control functions specific to battery powering:
(1)
Battery backup:
Protects data in RAM.
(2) Battery distribution (main and auxiliary battery power supplies):
Ensures a more reliable battery backup.
(3) Charge control:
Prevents excess Ni-Cd battery charging.
(4) Power distribution:
Outputs the supply voltages only while the computer is in operation in order to minimize bat-
tery consumption.
(5) Low voltage detection:
Automatically changes the main battery to the auxiliary battery supply.
In addition, the computer is provided with a software automatic power-off feature which prevents
the battery from being discharged out if the computer is inadvertently left on.
2.1.1 Major Components
The MAPLE board has elements mounted on both the sides. A speaker and elements such as re-
sistor packages, etc. are mounted on one side, while elements such as connectors, switches, and
LSI chips, etc. are mounted on the opposite side as shown in Fig.
2-1.
Table
2-1
lists major
board elements together with a summary of their function.
2-1