PXD20RM Datasheet, PDF (249/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

• FRCfast: frequency of high frequency internal RC oscillator.
• FPLL: frequency of FMPLL clock.
8.6.5.1 Crystal clock monitor
If FOSC is smaller than FRCfast divided by 2^RCDIV. bits of CMU_CSR and the CK_FXOSC is ‘ON’ as
signalled by the MC_ME then:
• An event pending bit OLRI in CMU_ISR is set.
• A failure event OLR is signalled to the MC_RGM which in turn can automatically switch to a safe
fallback clock and generate an interrupt or a reset.
NOTE
F_XOSC must be greater than F_FIRC /
2^RCDIV by at least 0.5 MHz in order to guarantee correct
XOSC monitoring.
8.6.5.2 PLL clock monitor
The PLL clock CK_PLL frequency can be monitored by programming CME bit of CMU_CSR register to
‘1’. CK_PLL monitor starts as soon as CME bit is set. This monitor can be disabled at any time by writing
CME bit to ‘0’.
If CK_PLL frequency (FPLL) is greater than a reference value determined by the HFREF[11:0] bits of
CMU_HFREFR and the CK_PLL is ‘ON’ as signalled by the MC_ME then
• An event pending bit FHHI in CMU_ISR is set,
• A failure event is signalled to the MC_RGM and Fault Collection Unit which in turn can generate
an interrupt or a reset.
If FPLL is less than a reference clock frequency (FRC/4) and the CK_PLL is ‘ON’ as signalled by the
MC_ME then an event pending bit FLCI in CMU_ISR will be set.
If FPLL is less than a reference value determined by the LFREF[11:0] bits of CMU_LFREFR and the
CK_PLL is ‘ON’ as signalled by the MC_ME then
• An event pending bit FLLI in CMU_ISR is set,
• A failure event FLL is signalled to the MC_RGM which can generate an interrupt or a reset.
NOTE
F_PLL must be greater than F_FIRC / 4 by at least
0.5 MHz in order to guarantee correct PLL monitoring.
8.6.5.3 Frequency meter
The purpose of frequency meter is to calibrate the internal RC oscillator (CK_IRC) using a known
frequency.
Hint: This value can then be stored into the flash so that application software can reuse it later on.
Freescale Semiconductor
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
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