M Heimbach

PWM with TPM Timer at low frequency

Discussion created by M Heimbach on Feb 2, 2010
Latest reply on Feb 3, 2010 by M Heimbach

Hi,  I need a PWM function to use with a frequency of as low as a minute or two.  For example, a freq of 1 minute would provide a 30 secs on/30 secs off with a 50% duty cycle.  I'm using a 32.768kHz external crystal attached to the XTAL pins, and have a bus frequency of 4MHz.  Unfortunately, dividing the clock by 128 and doing a full count in the TPM counter 0xFFFF does not provide a sufficiently long time period. 

There is a statement in my user manual that an internal "XCLK" could be used.  After reading what I could find in this forum, I still cannot figure out if there's a way to provide a lower clock freq to the TPM without changing the bus clock frequency.  If using the "XCLK" is an option, any suggestions about what registers to alter to provide a lower clock freq for the TPM ?  I am using the HCS08LG32 (C coding).   Thanks.