SAB-C509-LM SIEMENS [Siemens Semiconductor Group], SAB-C509-LM Datasheet - Page 62

• Manufacturer Part Number: SAB-C509-LM
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Oscillator Watchdog
The oscillator watchdog of the C509-L serves for three functions :
Figure 35
Block Diagram of the Oscillator Watchdog
Semiconductor Group
– Monitoring of the on-chip oscillator's function.
– Restart from the hardware power down mode.
– Fast internal reset after power-on.
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 oscillatior to stabilize; then the oscillator watchdog
reset is released and the part starts program execution again.
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.
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.
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C509-L
09.96