Epson PX-8 Technical Manual page 85

REV.-A
2.5.2.5 SWS
SW5 is the Initial Reset switch which is used to initialize the entire computer including the sub-
CPU 7508. Normally, it is pressed when the system is first initialized and a message, "SYSTEM
INITIALIZE", is displayed on the LCD panel. This switch must also be pressed, however, when the
computer gets into a software loop or the sub-CPU stops operating for the same some reason
and, SW2 is ineffective.
The switch is an alternate singal-pole, double-throw type (containing contacts A and B). One con-
tact is connected to the reset (RS) input terminal of the sub-CPU for initializing it. The other one
(A4/5 in the circuit diagram) is inserted between the backup line power line from the auxiliary bat-
tery and the logic circuit voltage supply line. When the switch is pressed and this contact is
closed, the backup voltage, which is normally supplied through the transistor Q23, is directly fed
to the logic circuit voltage supply line, bypassing the transistor. This is required to slightly raise
the logic circuit supply voltage in order to ensure computer reinitialization in an abnormal condi-
tion. A hardware failure may have occurred if SW5 needs to be pressed.
2.5.3 Variable Resistors
Three variable resistors are located on the MAPLE board as shown in Fig. 2-61 and one each on
the LCD unit (MAP-LD board) and the microcassette tape drive (MAP-MC board), totalling five.
The functions of the individual variable resistors are detailed in the following.
2.5.3.1 MAPLE Board Variable Resistors
Table 2-12 lists the three variable resistors used on the MAPLE board together with their func-
tions.
Table 2-12 MAPLE Board Variable Resistors and Their Functions
Name Function
VR1 This variable resistor is used to control the output
(Circuit diagram coordination H7) sound level to the built-in and external (if used)
speakers.
VR2
Allows the user to adjust the reference voltage to the
((Circuit diagram coordination D5)
A-D converter (1 D). An incorrect adjustment of this re-
ference voltage may result in an error in voltage detec-
tion and A-D conversion of the barcode reader or ex-
ternal analog input signal by the sub-CPU.
VR3
Allows the user to adjust the frequency of the sub-CPU
(Circuit diagram coordination C6!7)
driving clock signal.
2-61