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Chapter 11 S12XE Clocks and Reset Generator (S12XECRGV1) Block Description
MC9S12XE-Family Reference Manual Rev. 1.07
Freescale Semiconductor
505
TheinternalresetoftheMCUremainsassertedwhiletheresetgeneratorcompletesthe192SYSCLKlong
reset sequence. In case the RESET pin is externally driven low for more than these 192 SYSCLK cycles
(External Reset), the internal reset remains asserted longer.
Figure 11-21. RESET Timing
11.5.1.1
Clock Monitor Reset
The S12XECRG generates a Clock Monitor Reset in case all of the following conditions are true:
Clock monitor is enabled (CME = 1)
Loss of clock is detected
Self-Clock Mode is disabled (SCME = 0).
The reset event asynchronously forces the configuration registers to their default settings. In detail the
CME and the SCME are reset to logical ‘1’ (which changes the state of the SCME bit. As a consequence
the S12XECRG immediately enters Self Clock Mode and starts its internal reset sequence. In parallel the
clock quality check starts. As soon as clock quality check indicates a valid Oscillator Clock the
S12XECRGswitchestoOSCCLKandleavesSelfClockMode.Sincetheclockqualitycheckerisrunning
in parallel to the reset generator, the S12XECRG may leave Self Clock Mode while still completing the
internal reset sequence.
11.5.1.2
Computer Operating Properly Watchdog (COP) Reset
When COP is enabled, the S12XECRG expects sequential write of $55 and $AA (in this order) to the
ARMCOPregisterduringtheselectedtime-outperiod.Oncethisisdone,theCOPtime-outperiodrestarts.
If the program fails to do this the S12XECRG will generate a reset.
) (
) (
)
(
)
SYSCLK
128+
n
cycles
with
n
being
min 3 / max 6
cycles depending
on internal
synchronization
delay
64 cycles
ICRG drives RESET pin low
possibly
SYSCLK
not
running
possibly
RESET
driven low
externally
)
(
(
RESET
RESET pin
released