21.4.2 Low Power Bit Usage
The C2[LP] bit is provided to allow the FLL to be disabled and thus conserve power
when these systems are not being used. The C4[DRST_DRS] can not be written while
C2[LP] bit is 1. However, in some applications, it may be desirable to enable the FLL
and allow it to lock for maximum accuracy before switching to an engaged mode. Do this
by writing C2[LP] to 0.
21.4.3 MCG Internal Reference Clocks
This module supports two internal reference clocks with nominal frequencies of 32 kHz
(slow IRC) and 4 MHz (fast IRC). The fast IRC frequency can be divided down by
programming of the FCRDIV to produce a frequency range of 32 kHz to 4 MHz.
21.4.3.1 MCG Internal Reference Clock
The MCG Internal Reference Clock (MCGIRCLK) provides a clock source for other on-
chip peripherals and is enabled when C1[IRCLKEN]=1. When enabled, MCGIRCLK is
driven by either the fast internal reference clock (4 MHz IRC which can be divided down
by the FRDIV factors) or the slow internal reference clock (32 kHz IRC). The IRCS
clock frequency can be re-targeted by trimming the period of its IRCS selected internal
reference clock. This can be done by writing a new trim value to the
C3[SCTRIM]:C4[SCFTRIM] bits when the slow IRC clock is selected or by writing a
new trim value to the C4[FCTRIM]:C2[FCFTRIM] bits when the fast IRC clock is
selected. The internal reference clock period is proportional to the trim value written.
C3[SCTRIM]:C4[SCFTRIM] (if C2[IRCS]=0) and C4[FCTRIM]:C2[FCFTRIM] (if
C2[IRCS]=1) bits affect the MCGOUTCLK frequency if the MCG is in FBI or BLPI
modes. C3[SCTRIM]:C4[SCFTRIM] (if C2[IRCS]=0) bits also affect the
MCGOUTCLK frequency if the MCG is in FEI mode.
Additionally, this clock can be enabled in Stop mode by setting C1[IRCLKEN] and
C1[IREFSTEN], otherwise this clock is disabled in Stop mode.
Functional Description
KL02 Sub-Family Reference Manual, Rev. 2.1, July 2013
278
Freescale Semiconductor, Inc.
