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3.5 Resets
3.5
Resets
The MB89980 series supports the following four types of reset source:
External reset
Software reset
Watchdog reset
Power-on reset (optional)
At reset, main clock oscillation stabilization delay time may or may not occur by the
operating mode and option settings.
s Reset Source
r External reset
Inputting an "L" level to the external reset pin (RST) generates an external reset. Returning the
reset pin to the "H" level wakes up the CPU from the external reset.
When power is turned on to products with power-on reset or for external resets in stop mode,
the reset operation is performed after the oscillation stabilization delay time has passed and the
CPU wakes up from the external reset. External resets on products without power-on reset do
not wait for the oscillation stabilization delay time.
The external reset pin can also function as a reset output pin (optional).
r Software reset
Writing "0" to the software reset bit in the standby control register (STBC: RST) generates a
four-instruction cycle reset. The software reset does not wait for the oscillation stabilization
delay time.
r Watchdog reset
The watchdog reset generates a four-instruction cycle reset if data is not written to the watchdog
timer control register (WDTC) within a fixed time after the watchdog timer starts. The watchdog
reset does not wait for the oscillation stabilization delay time.
Table 3.5-1 Reset Source
Reset source
Reset conditions
External reset
Set the external reset pin to the "L" level.
Software reset
Write "0" to the software reset bit in the standby control register (STBC:
RST).
Watchdog
reset
Watchdog timer overflow
Power-on reset
Power is turned on (only on products with a power-on reset).