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eQEP index error by rotary switch

Jan van Kuilenburg
Prodigy 60 points
Other Parts Discussed in Thread: TMS320F28069, MOTORWARE

I have a problem in the EQEP driver. EQEP is in Reset on Index Event mode (QEPCTL[PCRM]=00).

The encoder gives 1000 pulses. If I rotate it forward and backward around the index position, QPOSILAT will show 4 or 3995, not the correct vaule 0 or 3999. Then QEPSTS[PCEF] is set.

When i don't change the rotation, turns in the same direction, QPOSILAT value will be updated by Index  0  or 3999.

What do I wrong?

  • 0
    TI__Guru 57255 points

    Hi Jan,

    You did not comment on what device you are using.

    Regardless, there is a device errata describing the problem that you are seeing.  Please see the following advisory in your particular device's errata document:
    eQEP: Position Counter Incorrectly Reset on Direction Change During Index

    As described in the workarounds listed, and depending on the width of your index signal, it may be possible to use IEI to get around the issue.

    For example, a good solution for the situation where the width of I is 1/4 the period of A may be the following:  to set PCRM=2, IEI=2, and use the synchronization/qualification features inside the GPIO to delay I.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Prodigy 60 points
    Hi Brett,

    Thanks for your answer, it's now okay.

    The problem was also, when the direction change was not during the Index-puls. My Index is 1/4 period (A&B). The solution of this is only the timedelay with synchronization inside teh GPIO. Then the latch is working okay.

    When you have a direction change during the index-puls, you needs your complete solution. (Then is the latch not working)

    Sorry i forgot the device: TMS320F28069 (Piccolo) with motorware drivers.

    Thank you,
    Jan.