topic Re: external clock in pwm mode in 8-bit Microcontrollers

external clock in pwm mode

eaegalera — Thu, 21 Jun 2007 20:52:10 GMT

I am developing a project using 9S08QG4.
In my project I am using the following configuration for PWM:
TPMSC = 0B00001000;
TPMC0SC = 0B00101000;
TPMC0SC_ELS0B = 0;
TPMMOD = 100;
TPMC0V = 50;
This configuration perfectly works!
He happens that the need appeared of synchronizing my pwm with the electric (220V) net, then I changed the configuration of the TPMSC register for:
TPMSC = 0B00011000;
to use the pin TCLK as entrance of the clock of the connected pwm in the net. I verify with the oscilloscope and he has a wave of 3,2V of width and 60Hz of frequency in the pin TCLK but the out of the pwm channel doesn't alter. What this lacking?

Thank you

Re: external clock in pwm mode

bigmac — Thu, 21 Jun 2007 23:27:25 GMT

Hello,

If the following lines are actually used (for either TPM clock source), this will actually disable the timer channel output.

TPMC0SC = 0B00101000;
TPMC0SC_ELS0B = 0; /* PTA0 pin reverts to GPIO */

Be aware that, by using a 60Hz external clock, the PWM frequency will be 60/100 = 0.6Hz. I am not sure if this is your intention.

If you actually need to synchronise the edge of the output waveform to a zero-crossing of the 60Hz waveform, this is a somewhat different problem, probably involving input capture and output compare operations, rather than PWM.

Regards,

Mac

Message Edited by bigmac on 2007-06-22 02:29 AM