Hardware Reset Circuit - Panasonic JS-170FR Series Service Manual

2.1.9

Hardware reset circuit

MB3771 is used in the hardware reset circuit.
When this MB3771 is used, a low level is maintained at Pin 8 of the RESET output terminal under the condition that the power
supply voltage of VCC (Pin 5) is below the reference voltage (approx. 4.2V).
If the reference voltage is exceeded, the potential level at the RESET output terminal is turned high after the lapse of the
predetermined time period (approx. 100msec), according to the capacitance connected to Pin 1.
In addition to power supply voltage level check, the MB3771 functions to receive the forced reset signal from the outside.
If the following conditions are satisfied as the external factors, the potential level at Pin 6 of the MB3771 will be lowered. Then,
similarly as for the case when the power supply voltage is lowered, the potential level at Pin 8 of the RESET output terminal is
turned low.
{External factors}
• The RESETSW# signal is turned to the low level. (RESET switch pressed)
• ISARST# is turned to the low level. (During execution by software)
• The PWRGOOD signal is turned to the low level. (POWER switch turned off)
• VRMPGD is turned to the low level. (Supervision of CPU voltage)
• DBRESET#3 signal is turned to the low level. (In case of debug)
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