8-bit Microcontrollers中的主题 Re: How to select crystal and PLL settings to get high standard baud rates up to 921600 baud?

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

AndersJ — Sun, 09 Mar 2014 20:23:00 GMT

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

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

kef2 — Mon, 10 Mar 2014 20:28:26 GMT

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.

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

soli255 — Tue, 11 Mar 2014 21:52:55 GMT

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.

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

soli255 — Tue, 18 Mar 2014 18:03:27 GMT

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.