SAB80C517A-N18 Siemens Semiconductor Group, SAB80C517A-N18 Datasheet - Page 59

• Manufacturer Part Number: SAB80C517A-N18
• Description: 8-Bit CMOS Single-Chip Microcontroller
• Manufacturer: Siemens Semiconductor Group

Oscillator Watchdog
The unit serves three functions:
– Monitoring of the on-chip oscillator’s function.
– Restart from the Hardware Power Down Mode.
– Fast internal reset after power-on.
If the oscillator watchdog unit is to be used it must be enabled (this is done by applying high
level to the control pin OWE).
Figure 12 shows the block diagram of the oscillator watchdog unit. It consists of an internal RC
oscillator which provides the reference frequency of the on-chip oscillator. The RC oscillator
can be enabled/disabled by the control pin OWE. If it is disabled the complete unit has no
function.
Semiconductor Group
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 forced into reset; if the failure condition
disappears (i.e. the on-chip oscillator has again a higher frequency than the RC oscillator),
the part executes a final reset phase of appr. 0.25 ms in order to allow the oscillator
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
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.
watchdog function is only part of the complete Hardware Power Down sequence; however,
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SAB 80C517A/83C517A-5
1994-05-01