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Hercules RM48L952 Non-standard NHET/PWM waveforms and NHET/Pulse Capture

Tammy Noergaard
Genius 3665 points

Hi.

  We are using the Hercules Board with RM48L942 processor.  2 questions:

1. We have verified standard PWM requirements (except for 100% to 0% problem handled in another TI case).  Can we program the NHET/PWM on this processor to create non-standard waveforms -- triangular and sinewave

2. Can an NHET programmed for Pulse Capture do 100Hz over 1minute?

Thank you.

 

  • 0
    Prodigy 50 points
    1. create the (sinewave) waveform in RAM, then use the HTU to transfer it into the NHET program at a certain frequency.
  • 0 in reply to Raik Strohbach
    Genius 3665 points
    Hi Thank you. One the non-standard waveforms, what do you mean? Does TI have a simple psudocode example to illustrate? Do we still configure the HET terminal as a PWM? Thank you again.
  • 0 in reply to Tammy Noergaard
    TI__Guru 68920 points

    Tammy,

    For a triangle wave or sinusoid,  you have two options that I'm aware of:

    1) add some form of DAC to the TMS570 - could be simply some resistor network or could be an IC..

    2) use a PWM to approximate the waveform with the addition of an external low pass filter (could be simply an R-C network)


    For (2) one of the Hercules Forum's 'Rising Stars' Martin Valencia  posted a write-up here:  

    Now regarding the waveform information.  For a triangle wave - the HET could generate the digital sequence locally.  It has the ability to add and subtract as well as count,  so you can program a starting duty cycle, ending duty cycle and update rate into the HET and let it generate the triangle automatically.   

    For the sinusoid I suppose it depends on how clean a sinusoid you need.   You could store a table of PWM periods representing the SINUSOID in flash and then use the CPU  (or HTU) to fetch the values into HET.   If you don't need a super clean sinusoid you could probably store a small table in N2HET RAM and interpolate linearly between the points.    You have to low pass filter anyway to convert the PWM into a sinusoid so that process may also clean up the interpolation.      If I had to figure this out I'd probably start experimenting in MATLAB/SIMULINK first, as a lot depends on the frequency range you are generating (compared to the PWM frequency of the HET) and how clean an output you required.    You can model the filter in MATLAB/SIMULINK and get a spectrum of the output very easily.