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F2802x HRPWM "FF" value doesn't work



I'm using the F28027 controlCARD with the evaluation board.

 

In my program, I'm updating the duty cycle of the HRPWM for a DAC.  The HRPWM extra 8 bits (CMPAHR) seem to have a problem though - whenever it is equal to 0xFF the HRPWM generator stops toggling and stays low.

 

It appears to be the register itself, and not the way I'm changing the value.  I have the watch window displaying:

EPwm1Regs.CMPA.all

and I can pause the program to enter new values.

 

I was checking 50% duty cycle accuracy when I noticed this.  The values:

0x7FFF FE00

0x8000 0000

both work, but

0x7FFF FF00

does not.

 

With some experimentation, it seems that no matter what the ePWM duty cycle is, if the HRPWM register portion is "FF" the PWM stops toggling.  For example:

Works:

0x5C26 FE00

0x5C27 0000

 

Doesn't work:

0x5C26 FF00

 

Something I could be doing wrong?