Power Off Detector Circuit; Print Head Driver Circuit - Epson LQ-670 Service Manual

LQ-670 Service Manual

2.2.2.4 Power Off Detector Circuit

Power-Down signal from the power supply board is sent to the port INTO of the CPU. The CPU initializes
the port P26 and sends a signal to the manual reset port MRES in the Reset IC(IC12) in order to let IC12
to output the reset signal.(Refer to Figure 2-9) When the Power Down signal breaks into during the waiting
mode, the CPU considers it as POWER-OFF immediately and performs POWER-OFF operation. If Power
Down signal breaks into during the printing operation, the CPU stops printing immediately and checks if
the Power Down signal is output after a certain time passed, which is about 10ms. If the Power-Down
signal is output, the CPU considers it as POWER OFF and performs POWER OFF operation.
After the POWER OFF is detected, the CPU holds at least 32 bite writing time for the EEPROM. After
writing is completed, the CPU reset the whole circuit system by setting the port P26 "HIGH".

2.2.2.5 Print Head Driver Circuit

The print head driver circuit of this printer consists of the gate array, NPN transistor with Zener Diode built
in and print head. Also, this circuit outputs the print signal from the port HD1 HD24 in the gate array to the
transistor and drives the print head. The built in Zener Diode absorbs back electromotive force, which is
caused by the coil of the print head.
Figure 2-12. Print Head Driver Circuit
2-15
Rev. A