PC912XDP512F0CALR datasheet(80/1348 Pages) FREESCALE

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Chapter 2 Clocks and Reset Generator (S12CRGV6)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

2.1.2

Modes of Operation

This subsection lists and brieﬂy describes all operating modes supported by the CRG.

•

Run mode

All functional parts of the CRG are running during normal run mode. If RTI or COP functionality

is required, the individual bits of the associated rate select registers (COPCTL, RTICTL) have to

be set to a nonzero value.

•

Wait mode

In this mode, the PLL can be disabled automatically depending on the PLLSEL bit in the CLKSEL

•

Stop mode

Depending on the setting of the PSTP bit, stop mode can be differentiated between full stop mode

(PSTP = 0) and pseudo stop mode (PSTP = 1).

— Full stop mode

The oscillator is disabled and thus all system and core clocks are stopped. The COP and the

RTI remain frozen.

— Pseudo stop mode

The oscillator continues to run and most of the system and core clocks are stopped. If the

respective enable bits are set, the COP and RTI will continue to run, or else they remain frozen.

•

Self clock mode

Self clock mode will be entered if the clock monitor enable bit (CME) and the self clock mode

enable bit (SCME) are both asserted and the clock monitor in the oscillator block detects a loss of

clock. As soon as self clock mode is entered, the CRG starts to perform a clock quality check. Self

clock mode remains active until the clock quality check indicates that the required quality of the

incoming clock signal is met (frequency and amplitude). Self clock mode should be used for safety

purposes only. It provides reduced functionality to the MCU in case a loss of clock is causing

severe system conditions.

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