SAB80C515A-5 Datasheet, PDF (50/108 Pages) Siemens Semiconductor Group – 8-Bit CMOS Single-Chip Microcontroller Family

On-Chip Peripheral Components
5.3.2 Oscillator Watchdog Unit
The unit serves 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 executes a final reset
phase of appr. 0.5 ms in order to allow the oscillator to stabilize; then the oscillator watchdog
reset is released and the part starts program execution again.
– Restart from the Hardware Power Down Mode.
If the Hardware Power Down Mode is terminated the oscillator watchdog has to control the
correct start-up of the on-chip oscillator and to restart the program. The oscillator watchdog
function is only part of the complete Hardware Power Down sequence; however, the
watchdog works identically to the monitoring function. The Hardware Power Down Mode is
discussed in detail in section 4.1, 4.2
– Fast internal reset after power-on.
In this function the oscillator watchdog unit provides a clock supply for the reset before the on-
chip oscillator has started. In this case the oscillator watchdog unit also works identically to the
monitoring function. The power-on is described in section 4.3.
Note:
The oscillator watchdog unit is always enabled.
Semiconductor Group
5-17