C167CS-L datasheet(38/81 Pages) INFINEON

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C167CS-4R

C167CS-L

Data Sheet

V2.2, 2001-08

Oscillator Watchdog

The Oscillator Watchdog (OWD) monitors the clock signal generated by the on-chip

oscillator (either with a crystal or via external clock drive). For this operation the PLL

provides a clock signal which is used to supervise transitions on the oscillator clock. This

PLL clock is independent from the XTAL1 clock. When the expected oscillator clock

transitions are missing the OWD activates the PLL Unlock/OWD interrupt node and

supplies the CPU with the PLL clock signal. Under these circumstances the PLL will

oscillate with its basic frequency.

In direct drive mode the PLL base frequency is used directly (

fCPU = 2 … 5 MHz).

In prescaler mode the PLL base frequency is divided by 2 (

fCPU = 1 … 2.5 MHz).

Note: The CPU clock source is only switched back to the oscillator clock after a

hardware reset.

The oscillator watchdog can be disabled by setting bit OWDDIS in register SYSCON.

In this case (OWDDIS = ‘1’) the PLL remains idle and provides no clock signal, while the

CPU clock signal is derived directly from the oscillator clock or via prescaler or SDD. Also

no interrupt request will be generated in case of a missing oscillator clock.

Note: At the end of a reset bit OWDDIS reflects the inverted level of pin RD at that time.

Thus the oscillator watchdog may also be disabled via hardware by (externally)

pulling the RD line low upon a reset, similar to the standard reset configuration via

PORT0.

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