Not getting correct timing with PLL on MCF51MM.

robynyost — Fri, 03 Jun 2016 20:18:19 GMT

Nevermind - it was my timer that was off....

I have a 16MHz crystal attached to XTAL2 pin. I want a bus speed of 8MHz.

I set the PLL with:

// Initialize the clock

// Configure the XOSC1 clock

CCSCTRL = 0x08; // XOSC1 at low frequency, low power, inactive, use oscillator, select XOCS2 as input

MCGC2 = 0x36 // Divide by 1, high frequency, high gain, FLL not disable in bypass,

// use oscillator, clock active, clock disabled in stop.

// Wait until external reference is stable

while (MCGSC_OSCINIT == 0) ;

// Set the PEE

MCGC3 |= 0x10; // set DIV32 (bit 4) in MCGC3

MCGC1 = 0x98; // external clock, divide by 256

// Wait until the external reference is selected

while (MCGSC_IREFST != 0) ;

// Wait until external clock is selected as a bus clock reference

while ((MCGSC_CLKST) != 2) ;

MCGC3 = 0x52; // Set PLL (PLL ref divider of 16), leave DIB32 (not used in PLL), VDIV = 2, (multiply by 8)

while (MCGSC_PLLST == 0);

while (MCGSC_LOCK == 0);

MCGC1 = 0x18;

while (MCGSC_CLKST != 3);

I have a timer and toggle an output in that timer. Using the oscilloscope, I see the timer values are all off. Am I setting up the PLL wrong?

Re: Not getting correct timing with PLL on MCF51MM.

miduo — Mon, 31 Oct 2016 08:30:49 GMT

Hi,

From the sample code you provide, it seems no error. Did you have any progress on this issue?