Epson U375 - TM B/W Dot-matrix Printer, Technical Manual

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2-18
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Control circuitry
Reset circuit
The reset circuit is used to prevent the CPU from operating
erratically and the print head from printing unexpectedly
during the period of unstable voltage immediately after the
power is turned on. To accomplish this, the OUT terminal
output (pin 6) of the reset IC (U4) is supplied to the CPU
(U12) as the RESET input signal (pin 28), and is supplied
to the gate array (U19) as the RESET input signal (pin 1).
The output (pin 6) is also supplied as the switching signal
for controlling the +24V power supply circuitry.
The reset IC (U4) monitors the +5V voltage; when the
voltage is 4.5V or more, the reset is released for the CPU
and other components and the printer becomes ready.
In addition, the C terminal (pin 5) of the reset IC (U4) is
connected to the reset signal (CN9 #9) from IM-403 or the
reset signal (the DSR signal or pin 25 input signal) from the
host interface (CN2) via DIP switches 1-7 and 1-8. If a reset
signal is applied to this pin for at least 1ms, the reset IC
output goes low and the CPU and other components are
reset.
Refer to Chapter 7 for the reset circuit description and the
diagram for the TM-U375P.
Figure 2-41. Reset Circuit
CONFIDENTIAL