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The internal reference will stabilize in t
irefsts
microseconds before the FLL can acquire
lock. As soon as the internal reference is stable, the FLL will acquire lock in t
fll_acquire
milliseconds.
25.5.1.1 Initializing the MCG
Because the MCG comes out of reset in FEI mode, the only MCG modes that can be
directly switched to upon reset are FEE, FBE, and FBI modes (see
).
Reaching any of the other modes requires first configuring the MCG for one of these
three intermediate modes. Care must be taken to check relevant status bits in the MCG
status register reflecting all configuration changes within each mode.
To change from FEI mode to FEE or FBE modes, follow this procedure:
1. Enable the external clock source by setting the appropriate bits in C2 register.
2. Write to C1 register to select the clock mode.
• If entering FEE mode, set C1[FRDIV] appropriately, clear C1[IREFS] bit to
switch to the external reference, and leave C1[CLKS] at 2'b00 so that the output
of the FLL is selected as the system clock source.
• If entering FBE, clear C1[IREFS] to switch to the external reference and change
C1[CLKS] to 2'b10 so that the external reference clock is selected as the system
clock source. The C1[FRDIV] bits should also be set appropriately here
according to the external reference frequency to keep the FLL reference clock in
the range of 31.25 kHz to 39.0625 kHz. Although the FLL is bypassed, it is still
on in FBE mode.
• The internal reference can optionally be kept running by setting C1[IRCLKEN].
This is useful if the application will switch back and forth between internal and
external modes. For minimum power consumption, leave the internal reference
disabled while in an external clock mode.
3. Once the proper configuration bits have been set, wait for the affected bits in the
MCG status register to be changed appropriately, reflecting that the MCG has moved
into the proper mode.
• If the MCG is in FEE, FBE, PEE, PBE, or BLPE mode, and C2[EREFS] was
also set in step 1, wait here for S[OSCINIT0] bit to become set indicating that
the external clock source has finished its initialization cycles and stabilized.
Chapter 25 Multipurpose Clock Generator (MCG)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors
565
Содержание K22F series
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Страница 168: ...Module clocks K22F Sub Family Reference Manual Rev 4 08 2016 168 NXP Semiconductors...
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Страница 1040: ...Example configuration for chained timers K22F Sub Family Reference Manual Rev 4 08 2016 1040 NXP Semiconductors...
Страница 1118: ...Device mode IRC48 operation K22F Sub Family Reference Manual Rev 4 08 2016 1118 NXP Semiconductors...
Страница 1122: ...USB Voltage Regulator Module Signal Descriptions K22F Sub Family Reference Manual Rev 4 08 2016 1122 NXP Semiconductors...
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