Datasheet

C505/C505C/C505A/C505CA
Data Sheet 47 12.00
Oscillator Watchdog
The oscillator watchdog unit serves for three functions:
– Monitoring of the on-chip oscillator's function
The watchdog supervises the on-chip oscillator's frequency; if it is lower than the frequency
of the auxiliary RC oscillator in the watchdog unit, the internal clock is supplied by the RC
oscillator and the device is brought into reset; if the failure condition disappears (i.e. the on-
chip oscillator has a higher frequency than the RC oscillator), the part, in order to allow the
oscillator to stabilize, executes a final reset phase of typ. 1 ms; then the oscillator watchdog
reset is released and the part starts program execution from address 0000
H
again.
– Fast internal reset after power-on
The oscillator watchdog unit provides a clock supply for the reset before the on-chip oscillator
has started. The oscillator watchdog unit also works identically to the monitoring function.
– Control of external wake-up from software power-down mode
When the power-down mode is left by a low level at the P3.2/INT0
pin or the P4.1/RXDC pin,
the oscillator watchdog unit assures that the microcontroller resumes operation (execution of
the power-down wake-up interrupt) with the nominal clock rate. In the power-down mode the
RC oscillator and the on-chip oscillator are stopped. Both oscillators are started again when
power-down mode is released. When the on-chip oscillator has a higher frequency than the
RC oscillator, the microcontroller starts program execution by processing a power down
interrupt after a final delay of typ. 1 ms in order to allow the on-chip oscillator to stabilize.