Service manual

Rev. B Mechanism Configuration and Operating Principles 2-17
TM-U200 Series (Type B) Service Manual
Confidential
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 power is turned
on. To accomplish this, the OUT terminal output (pin 5) of the reset IC (U9) is supplied to the
CPU (U5) as the RESET
input signal (pin 21).
The reset IC (U9) monitors the +5 V voltage. When the voltage is 4.5 V or more, reset is released
for the CPU and other components, and the printer becomes ready.
In addition, the C terminal (pin 4) of the reset IC (U9) is connected to the reset signal (DSR signal
or pin 25 input signal) from the host interface via DIP switches 2-3 and 2-4. If a reset signal is
applied to this pin, reset IC output goes LOW and the CPU and other components are reset.
The reset signals differ, depending on the interface specifications:
RS-232 serial interface: Two signals can be selected (DSR signal or pin 25 input signal).
IEEE 1284 parallel interface: Pin 25 must be used for the RESET signal. DIP switch 2-4 is fixed
to ON. The printer can be reset with the Init
signal (pin 31) from
the host.
Figure 2-20 Reset circuit
Pin 29 of CN4 is the reset signal of the IEEE 1284 parallel interface circuit board.