Table of Contents
Advertisement
A "low" pulse applied to the reset interrupt input, pin 1 of the microprocessor U7D, causes the pro
cessor to restart execution of the printer operating system program stored in the ROM U8D, A reset
pulse occurs when the power is turned on. An external device connected to the serial bus can also
generate a reset, initializing all devices connected on the bus at the same time.
A short time after the power is turned on, the 5VDC supply rises to its normal operating level, This
forward biases Q21, allowing C3 to charge. When the voltage across C3 reaches 2 volts, the output
of the inverter U1C pin 6 goes "low", causing the output of the inverter U1C pin 4 to go "high".
This "low" pulse occurs when the unit is switched on. The reset input
—
RES
—
on the serial bus
(interface clear signal —IFC
—
on the 4023 IEEE interface) forces the reset pulse by applying a "low"
to the input of the inverter U1C pin 1.
CIRCUIT THEORY
RESET
Reset Logic Circuit Theory
POWER ON
+5V
-
Q21
COLLECTOR
Ui C5PIN
U1C6PIN
1
U1C4PIN
H
APPROX.
350 ms
Advertisement
Table of Contents
