Chapter 7 S12 Clock, Reset and Power Management Unit (S12CPMU_UHV_V5)
S12ZVHY/S12ZVHL Family Reference Manual, Rev. 1.05
Freescale Semiconductor
293
/* Procedure proposed by to setup PLL and Oscillator */
/* example for OSC = 4 MHz and Bus Clock = 25MHz, That is VCOCLK = 50MHz */
/* Initialize */
/* PLL Clock = 50 MHz, divide by one */
CPMUPOSTDIV = 0x00;
/* Generally: Whenever changing PLL reference clock (REFCLK) frequency to a higher value */
/* it is recommended to write CPMUSYNR = 0x00 in order to stay within specified */
/* maximum frequency of the MCU */
CPMUSYNR = 0x00;
/* configure PLL reference clock (REFCLK) for usage with Oscillator */
/* OSC=4MHz divide by 4 (
3
+1) = 1MHz, REFCLK range 1MHz to 2 MHz (REFFRQ[1:0] =
00
) */
CPMUREFDV = 0x
03
;
/* enable external Oscillator, switch PLL reference clock (REFCLK) to OSC */
CPMUOSC = 0x80;
/* multiply REFCLK = 1MHz by 2*(
24
+1)*1MHz = 50MHz */
/* VCO range 48 to 80 MHz (VCOFRQ[1:0] =
01
) */
CPMUSYNR = 0x
58
;
/* clear all flags, especially LOCKIF and OSCIF */
CPMUIFLG = 0xFF;
/* put your code to loop and wait for the LOCKIF and OSCIF or */
/* poll CPMUIFLG register until both UPOSC and LOCK status are “1” */
/* that is CPMIFLG == 0x1B */
/*...............continue to your main code execution here...............*/
/* in case later in your code you want to disable the Oscillator and use the */
/* 1MHz IRCCLK as PLL reference clock */
/* Generally: Whenever changing PLL reference clock (REFCLK) frequency to a higher value */
/* it is recommended to write CPMUSYNR = 0x00 in order to stay within specified */
/* maximum frequency of the MCU */
CPMUSYNR = 0x00;
/* disable OSC and switch PLL reference clock to IRC */
CPMUOSC = 0x00;
/* multiply REFCLK = 1MHz by 2*(
24
+1)*1MHz = 50MHz */
/* VCO range 48 to 80 MHz (VCOFRQ[1:0] =
01
) */
CPMUSYNR = 0x
58
;
/* clear all flags, especially LOCKIF and OSCIF */
CPMUIFLG = 0xFF;
/* put your code to loop and wait for the LOCKIF or */
/* poll CPMUIFLG register until both LOCK status is “1” */
/* that is CPMIFLG == 0x18 */
/*...............continue to your main code execution here...............*/
