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21.4.4 External Reference Clock
The MCG module can support an external reference clock in all modes. See the device
datasheet for external reference frequency range. When C1[IREFS] is set, the external
reference clock will not be used by the FLL. In these mode, the frequency can be equal to
the maximum frequency the chip-level timing specifications will support.
If any of the CME bits are asserted the slow internal reference clock is enabled along
with the enabled external clock monitor. For the case when C6[CME0]=1, a loss of clock
is detected if the OSC0 external reference falls below a minimum frequency (f
loc_high
or
f
loc_low
depending on C2[RANGE0]).
NOTE
All clock monitors must be disabled before entering these low-
power modes: Stop, VLPS, VLPR, VLPW, and VLLSx.
Upon detect of a loss of clock event, the MCU generates a system reset if the respective
LOCRE bit is set. Otherwise the MCG sets the respective LOCS bit and the MCG
generates a LOCS interrupt request.
21.4.5 MCG Fixed frequency clock
The MCG Fixed Frequency Clock (MCGFFCLK) provides a fixed frequency clock
source for other on-chip peripherals; see the block diagram. This clock is driven by either
the slow clock from the internal reference clock generator or the external reference clock
from the Crystal Oscillator, divided by the FLL reference clock divider. The source of
MCGFFCLK is selected by C1[IREFS].
This clock is synchronized to the peripheral bus clock and is valid only when its
frequency is not more than 1/8 of the MCGOUTCLK frequency. When it is not valid, it is
disabled and held high. The MCGFFCLK is not available when the MCG is in BLPI
mode. This clock is also disabled in Stop mode. The FLL reference clock must be set
within the valid frequency range for the MCGFFCLK.
21.4.6 MCG Auto TRIM (ATM)
The MCG Auto Trim (ATM) is a MCG feature that when enabled, it configures the MCG
hardware to automatically trim the MCG Internal Reference Clocks using an external
clock as a reference. The selection between which MCG IRC clock gets tested and
Chapter 21 Multipurpose Clock Generator (MCG)
KL02 Sub-Family Reference Manual, Rev. 2.1, July 2013
Freescale Semiconductor, Inc.
279
Содержание KKL02Z32CAF4R
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