NXP Semiconductors K22F series, Reference Manual, Page: 566 / 1407

• If in FEE mode, check to make sure S[IREFST] is cleared before moving on.
• If in FBE mode, check to make sure S[IREFST] is cleared and S[CLKST] bits
have changed to 2'b10 indicating the external reference clock has been
appropriately selected. Although the FLL is bypassed, it is still on in FBE mode.
4. Write to the C4 register to determine the DCO output (MCGFLLCLK) frequency
range.
• By default, with C4[DMX32] cleared to 0, the FLL multiplier for the DCO
output is 640. For greater flexibility, if a mid-low-range FLL multiplier of 1280
is desired instead, set C4[DRST_DRS] bits to 2'b01 for a DCO output frequency
of 40 MHz. If a mid high-range FLL multiplier of 1920 is desired instead, set the
C4[DRST_DRS] bits to 2'b10 for a DCO output frequency of 60 MHz. If a high-
range FLL multiplier of 2560 is desired instead, set the C4[DRST_DRS] bits to
2'b11 for a DCO output frequency of 80 MHz.
• When using a 32.768 kHz external reference, if the maximum low-range DCO
frequency that can be achieved with a 32.768 kHz reference is desired, set
C4[DRST_DRS] bits to 2'b00 and set C4[DMX32] bit to 1. The resulting DCO
output (MCGOUTCLK) frequency with the new multiplier of 732 will be 24
MHz.
• When using a 32.768 kHz external reference, if the maximum mid-range DCO
frequency that can be achieved with a 32.768 kHz reference is desired, set
C4[DRST_DRS] bits to 2'b01 and set C4[DMX32] bit to 1. The resulting DCO
output (MCGOUTCLK) frequency with the new multiplier of 1464 will be 48
MHz.
• When using a 32.768 kHz external reference, if the maximum mid high-range
DCO frequency that can be achieved with a 32.768 kHz reference is desired, set
C4[DRST_DRS] bits to 2'b10 and set C4[DMX32] bit to 1. The resulting DCO
output (MCGOUTCLK) frequency with the new multiplier of 2197 will be 72
MHz.
• When using a 32.768 kHz external reference, if the maximum high-range DCO
frequency that can be achieved with a 32.768 kHz reference is desired, set
C4[DRST_DRS] bits to 2'b11 and set C4[DMX32] bit to 1. The resulting DCO
output (MCGOUTCLK) frequency with the new multiplier of 2929 will be 96
MHz.
5. Wait for the FLL lock time to guarantee FLL is running at new C4[DRST_DRS] and
C4[DMX32] programmed frequency.
To change from FEI clock mode to FBI clock mode, follow this procedure:
Initialization / Application information
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
566 NXP Semiconductors