How to select crystal and PLL settings to get high standard baud rates up to 921600 baud?

[AndersJ]

HCS08.

Are there any tools available to help selecting the crystal and PLL settings

for standard baud rates, and specifically the higher ones, up to 921600 baud?

Anders J

[soli255]

Hello,

I am having same problem and until now I have no solution. Only an external resonator on 29,4912 MHz (BUS clock will be 14,7456 MHz) http://cz.farnell.com/abracon/asem1-29-4912mhz-lc-t/mems-oscillator-29-4912mhz-smd/dp/1633615 But I will also be glad for some crystal and FLL solution if somebody has it.

[soli255]

Hello,

now I already upgrade my hardware with external oscillator of 29.4912 MHz and run it as clock source by code:

  uint i;

  // 29.4912MHz Oscillator

  // Fbus = ( Fext * 1 / BDIV ) / 2 => 14.7456MHz

  ICSC2_BDIV     = 0b00;    // 00 BDIV = 1

  ICSC2_LP       = 1;       // 1 FLL is disabled in bypass modes

  ICSC2_EREFS    = 0;       // 0 External Clock Source requested.

  // wait for stability of oscillator

  for ( i = 0 ; i < 10000 ; i++ );

  ICSC1_IREFS    = 0;       // 0 External reference clock selected.

  ICSC1_CLKS     = 0b10;    // 10 External reference clock is selected

My baud rate is 921600. I am using MC9S08QE16 device.

[kef2]

Minimum bus clock required for 921600 is 921600*16=14745600Hz.

You may use standard UART crystal frequencies like 3.6864MHz or 7.3728MHz and PLL multiply it to 14.7456MHz. Processor expert may help finding right PLL/FLL settings.