Reset Circuits - Epson Stylus Color 600 Service Manual

Chapter2 Operating Principles

2.2.2.1 Reset Circuits

The reset circuit prevents the CPU from running away, which is caused by the unstable voltage in the
logic line during the power ON/OFF. Also, this circuit monitors level of power voltage at the overloading
or malfunction on the circuit and manages the printer to operate normally, keeping the damage to the
printer minimum during the abnormal situations. On the C200 main board, 2 ICs are mounted ; IC for
monitoring the voltage level (logic line) and IC for monitoring the voltage level (power line) and both
are monitored by the gate array and CPU.
The figure below shows reset circuit block diagram with explanation on the next page.
1 6
P 8 5
3 0
+ 5 V
2
5
4
Figure 2-20. Reset Circuit Block Diagram
[PST592(IC8)]
The actual operation of the circuit is to keep outputting Low signal until +5V line goes up to +4.2V
when the power is on, and to cancel the reset signal with output of High signal when the voltage goes up
more than 4.2V.
[M51955(IC9)]
This IC also performs as monitor on the power line same as the reset IC for logic described above.
High/Low is judged at the 33.2V.
[Relation between IC8 and IC9]
Reset signal which is low and output by IC9 is input to the CPU and gate array and system reset operation
is performed. Also, this signal is detected on the IC9(IC for reset monitor, power line) and outputs the
same Low signal towards CPU/NMI terminal by being input to NC5.
2-23
Rev. A