C504 Datasheet, PDF (32/49 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

C504
Oscillator Watchdog
The oscillator watchdog of the C504 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 an auxiliary RC oscillator, the internal clock is supplied by this RC oscillator and the C504
is put into reset state; if the failure condition again disappears, the part executes a final reset
phase of typ. 1 ms in order to allow the oscillator to stabilize; then the oscillator watchdog reset
is released and the part starts program execution 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 INT0 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 operation after a final delay of typ. 1 ms in order to allow the on-chip
oscillator to stabilize.
Figure 14
Block Diagram of the Programmable Watchdog Timer
Semiconductor Group
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