MAC7200 datasheet(508/976 Pages) FREESCALE

508 / 976 page

Functional Description

MAC7200 Microcontroller Family Reference Manual, Rev. 2

430

Freescale Semiconductor

NOTE

Remember that in parallel to additional actions caused by Self Clock Mode

or Clock Monitor Reset1 handling, the clock quality checker continues to

check the OSCCLK signal.

NOTE

The Clock Quality Checker enables the PLL and the voltage regulator

(VREG) anytime a clock check has to be performed. An ongoing clock

quality check could also cause a running PLL (fSCM) and an active VREG

during Doze Mode

23.4.2.5

Software Watchdog Timer (SWT)

The SWT (free running watchdog timer) allows the user to check that a program is running and sequencing

properly. This watchdog timer resides on the ARM platform. However, the CRG module provides the

clock for the watchdog timer.

23.4.2.6

Real Time Interrupt (RTI)

The RTI (real time interrupt) is in a separate module. However, the CRG module provides a special RTI

clock. This is a gated OSCCLK.

23.4.3

Operating Modes

23.4.3.1

Normal Mode

The CRG block behaves as described within this specification in all normal modes.

23.4.3.2

Self Clock Mode

The VCO has a minimum operating frequency, fSCM. If the external clock frequency is not available due

to a failure or due to long crystal start-up time, the Peripheral Bus Clock and the System Clock are derived

from the VCO running at the minimum operating frequency; this mode of operation is called Self Clock

Mode. This requires CME=1 and CMRD=1. If the MCU was clocked by the PLL clock prior to entering

Self Clock Mode, the PLLSEL bit will be cleared. If the external clock signal has stabilized again, the CRG

will automatically select OSCCLK to be the system clock and return to normal mode. Section 23.4.2.4,

“Clock Quality Checker,” for more information on entering and leaving Self Clock Mode.

NOTE

In order to detect a potential clock loss, the CME bit should be always

enabled (CME=1).

A Clock Monitor Reset will always set the CMRD bit to logical’1’

MAC7200 Datasheet(PDF) 508 Page - Freescale Semiconductor, Inc