Freescale Semiconductor MC9S12ZVM series, Справочное руководство

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Chapter 8 S12 Clock, Reset and Power Management Unit (S12CPMU_UHV_V6)
MC9S12ZVM Family Reference Manual Rev. 1.3
306 Freescale Semiconductor
/* 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...............*/