MAC7200 datasheet(139/976 Pages) FREESCALE

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Clock Generation

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

generated clock (in Self Clock Mode only). This allows these functions to continue to run during low

power operating modes if required. Refer to Chapter 26, “Periodic Interrupt Timer (PIT_RTI)” and

Chapter 13, “Miscellaneous Control Module (MCM)” for more information on these modules.

In order to ensure the presence of the clock, the MCU includes an on-chip hardware Crystal Monitor

connected to the output of the Oscillator, OSCCLK. The Crystal Monitor can be configured to invoke the

PLL self clocking mode or to generate a System Reset to time out as a result of no OSCCLK being present.

In addition to the Crystal Monitor, the MCU also provides a Clock Quality checker which performs a more

accurate check of the clock. The Clock Quality Checker counts a predetermined number of clock edges

within a defined time window to ensure that the clock is running. The checker can be invoked following

specific events such as wake-up or a Crystal Monitor failure.

5.2

Clock Generation

Figure 5-2 and Figure 5-3 shows the clock outputs and gating in the CRG. The effect of the different Low

Power modes on the various clocks is discussed in Chapter 3, “Low Power Modes”.

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