Malfunction Protective Circuit; Ga Operation Monitor; Cpu Operation Monitor; Mechanism Malfunction Monitor - Epson TM-U675 Service Manual

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Malfunction Protective Circuit

This printer has the following three malfunction protection functions:

GA operation monitor

The CPU (U3) monitors GA clock oscillation. The CPU firmware reads a specific GA register at
an arbitrary time, and compares that value with the value previously read. If the results of the
comparison are different, the system is judged to be operating normally. The GA changes the
register value using clock oscillation. Therefore, if it is operating normally, the register value
continuously changes.

CPU operation monitor

CPU runaway causes a WDT (watch dog timer) overflow, resulting in output of LOW status
from the CPU WDT output terminal. This is connected to the GA TIMI input terminal, and
when the GA detects the LOW status for a certain time, it goes to the reset status and is not
restored.

Mechanism malfunction monitor

When the thermal head becomes abnormally hot, the GA TIMI input terminal goes LOW, and
the GA is reset and is not restored. The firmware judges this as a GA malfunction, and processes
it as an unrecoverable error.
GA TIMI input terminal also goes LOW when the impact head becomes abnormally hot, causing
the GA to go to the reset status, which will not be restored. The firmware judges this as a GA
malfunction, and processes it as an unrecoverable error.
Appendix D-70 Product Overview Rev.D