NXP Semiconductors K22F series, Reference Manual, Page: 158 / 1407

• the core/system, FlexBus, and bus clocks are less than or equal to 4 MHz, and
• the flash memory clock is less than or equal to 1 MHz
NOTE
When the MCG is in BLPI and clocking is derived from the
Fast IRC, the clock divider controls, MCG_SC[FCRDIV] and
SIM_CLKDIV1[OUTDIV4], must be programmed such that
the resulting flash clock nominal frequency is 800 kHz or less.
In this case, one example of correct configuration is
MCG_SC[FCRDIV]=000b and
SIM_CLKDIV1[OUTDIV4]=0100b, resulting in a divide by 5
setting.
5.6 Clock Gating
The clock to each module can be individually gated on and off using the SIM module's
SCGCx registers. These bits are cleared after any reset, which disables the clock to the
corresponding module to conserve power. Prior to initializing a module, set the
corresponding bit in SCGCx register to enable the clock. Before turning off the clock,
make sure to disable the module.
Any bus access to a peripheral that has its clock disabled generates an error termination.
5.7 Module clocks
The following table summarizes the clocks associated with each module.
Table 5-2. Module clocks
Module Bus interface clock Internal clocks I/O interface clocks
Core modules
ARM Cortex-M4 core System clock Core clock —
NVIC System clock — —
DAP System clock — —
ITM System clock — —
cJTAG, JTAGC — — JTAG_CLK
System modules
DMA System clock — —
DMA Mux Bus clock — —
Port control Bus clock LPO —
Table continues on the next page...
Clock Gating
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
158 NXP Semiconductors