NXP Semiconductors K22F series - Page 570

a. BLPE: If a transition through BLPE mode is desired, first set C2[LP] to 1.
b. BLPE/PBE: C6 = 0x40
• C6[PLLS] set to 1, selects the PLL. At this time, with a C1[PRDIV] value of
2'b001, the PLL reference divider is 2 (see PLL External Reference Divide
Factor table), resulting in a reference frequency of 4 MHz/ 2 = 2 MHz. In
BLPE mode, changing the C6[PLLS] bit only prepares the MCG for PLL
usage in PBE mode.
• C6[VDIV] set to 5'b00000, or multiply-by-24 because 2 MHz reference * 24
= 48 MHz. In BLPE mode, the configuration of the VDIV bits does not
matter because the PLL is disabled. Changing them only sets up the multiply
value for PLL usage in PBE mode.
c. BLPE: If transitioning through BLPE mode, clear C2[LP] to 0 here to switch to
PBE mode.
d. PBE: Loop until S[PLLST] is set, indicating that the current source for the PLLS
clock is the PLL.
e. PBE: Then loop until S[LOCK0] is set, indicating that the PLL has acquired
lock.
4. Lastly, PBE mode transitions into PEE mode:
a. C1 = 0x10
• C1[CLKS] set to 2'b00 to select the output of the PLL as the system clock
source.
b. Loop until S[CLKST] are 2'b11, indicating that the PLL output is selected to
feed MCGOUTCLK in the current clock mode.
• Now, with PRDIV of divide-by-2, and C6[VDIV] of multiply-by-24,
MCGOUTCLK = [(4 MHz / 2) * 24] = 48 MHz.
Initialization / Application information
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
570 NXP Semiconductors