TMS320F28335 PWM question - Polarity for off state setting

We are using the TI DSP TMS320F28335PGFA. This DSP was used to control a PWM inverter. Both EPWMA and EPWMB modules are used. Total 12 PWM channels.

In our latest design, we selected logic 1 as the off state for these PWM channels. Is this acceptable for F28335? Or is it required to set the off state of the PWM to logic 0 only? It seems that all TI reference design was using logic 0 as off state for the PWM.

Since the board is going to be used for inverter control, the PWM outputs need to be in either off state or high impedance state when we reprogram the DSP. We could either re-program thru JTAG or serial port.

During reprogramming, can the off state or high impedance state of the PWM outputs be guaranteed? 

Thanks - Bruce

  • Bruce,

    >> In our latest design, we selected logic 1 as the off state for these PWM channels. Is this acceptable for F28335? Or is it required to set the off state of the PWM to logic 0 only?

    You can configure the off-state as you want, either hi or lo.  This is done using the Action Qualifier Output registers (AQCTLA and AQCTLB) in each ePWM module.

    >> During reprogramming, can the off state or high impedance state of the PWM outputs be guaranteed?

    Flash programming utilities have no reason to touch the PWMs (GPIO pins).  I'd expect that they will stay in whatever state you have them in prior to starting the programming.  Best thing to do is reset the device before programming.  The will set the PWMs as GPIO inputs (hi-Z).

     

    Regards,

    David