C505-2RM SIEMENS [Siemens Semiconductor Group], C505-2RM Datasheet - Page 49

• Manufacturer Part Number: C505-2RM
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

Oscillator Watchdog
The oscillator watchdog unit serves for three functions:
Semiconductor Group
– Monitoring of the on-chip oscillator's function
– Fast internal reset after power-on
– Control of external wake-up from software power-down mode
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.
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.
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.
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C505A / C505CA
C505 / C505C
1997-12-01