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MC9S12G64: Using external oscillator (not crystal)

Question asked by William Deshaies on Jun 7, 2013
Latest reply on Jun 12, 2013 by bigmac

Hi everyone,


I'm trying to use an external oscillator for the G64. The source is an RF chip that give me 13.56MHz. I calculate all the value for the CPMUSYNR, CPMUREFDIV but the PLL never lock. By going backward, I find that the bit CPMUFLG_UPOSC is always zero. Like if the micro doesn't detect the oscillation.


The clock source is plug to the EXTAL pin and XTAL pin is not plug.


Do I have some register to set for the UPOSC bit to go 1 or it's just not possible with this clock configuration?


Here is my code for now:

CPMUOSC = 0x80; //Enable oscillator

CPMUSYNR = 0x16; // VCO from 32 to 48MHz, SYNDIV = 22

CPMUREFDIV = 0x0C; // Fref from 1 to 2MHz, Fref = Fosc/13

while(!CPMUFLG_LOCK); // Wait for lock !!! Stop here !!!

CPMUCLKS_PLLSEL = 1; //Switch to PLL


Thanks you