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Pseudo STOP mode can be used with the RTI enabled to provide a time base within a low power mode.
This is described in chapter 7 of the Reference Manual S12XHZ-RM
Pseudo STOP mode is selected as opposed to STOP mode by setting the PSTP bit. Then when the CPU executes the STOP instruction, the device enters pseudo STOP mode instead of STOP mode. In pseudo STOP mode the oscillator continues operating....
Setting PSTP in the CLKSEL register ensures that the oscillator continues (pseudo STOP instead of STOP mode).
Setting PRE in the PLLCTL register enables the RTI in pseudo STOP
Register RTICTL is used to set the RTI rate.
RTIE in the register CRGINT enables the interrupt.
Ensure also that the CPU CCR S bit is clear for (pseudo) STOP mode entry.
DPB
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