Reset By +5V Line Voltage Detection; Protection Circuit - Star Micronics NX-1020 Technical Manual

THEORY OF OPERATION

2-4. Reset by +5V Line Voltage Detection

A voltage-detecting IC (IC3 in Fig. 2-14) detects momentary drops in voltage or unstable voltage supply (due to power
failures, etc.) on the +5V line. If the voltage on the +5V line falls below 4.25V, the RESET signal appears at the output
terminal of the voltage-detecting IC.
Fig. 2-16 Operational Timing Chart
Fig. 2-15 Equivalent Circuit of
Voltage-Detecting IC

2-5. Protection Circuit

This printer is provided with a protection circuit which shuts off the print head and motor driving circuits in the event of
a CPU malfunction. (Refer to Fig.2-14)
The CPU normally outputs a LOW level signal from the terminal (WD OUT).
However, if the CPU malfunctions, it can not output this signal.
When the LOW level signal is not output from the CPU, the input terminal (Cd) of the voltage-detecting IC goes to LOW
and the RESET signal is output from the output terminal (OUT) of the voltage-detecting IC. By this signal, the CPU and
the gate array are reset; and the print head, the carriage motor and paper feed motor driving signals are ignored, protecting
the printer from the CPU runaway.
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