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LAUNCHXL-F28069M: F28069M and contacting rotary encoders

Manu Abraham
Genius 3510 points
Part Number: LAUNCHXL-F28069M

Hi,

I have one of these rotary contacting encoders.

In erstwhile use cases, I have successfully used the encoder with an interrupt on a GPIO monitoring Signal A & Signal B. 

Looking at the F28069, it does have a eQEP module which can handle a rotary encoder, but it uses additional signals too, in addition to the INDEX pulse.

Wondering whether it is possible to use the encoder mentioned, with eQEP module ?

Thanks,

Manu

  • 0
    Genius 3510 points
    Hi,

    Maybe I need to clarify a bit more, found my initial post to be a bit cryptic, reading it again myself.

    Trying to use the encoder to input values by turning the encoder CW or CCW by hand, like a potentiometer, rather than an encoder connected to a motor.

    Looking for a simple quadrature count mode as described in 7.3.1 Position Counter Input Modes, wondering how to go about it, if possible.

    I think the quadrature count mode would do it, but the Index pulse and the Strobe signals give me a bit of headache, as what to be done.


    Thanks,

    Manu
  • 0 in reply to Manu Abraham
    Expert 1710 points
    I'm not familiar with the chip you're using, but I am familiar with encoders.

    The encoder you selected has A, B, C terminals, plus a switch when you push the button down. Look near the end of the data sheet where it shows a suggested filter connection. That shows that A and B go to the A and B encoder inputs on your chip, and C is ground. You will not be using Index or Strobe.

    Lloyd
  • 0 in reply to lslonim
    Genius 3510 points
    Hi,

    I am not worried about the encoder, It has a QA & QB output as a you rightly pointed out.

    Not worried about the switch either. Previously I have used the same encoder with a microchip dspic using a LPF and connected with GPIO edge triggered interrupts, to count UP or DOWN. Worked acceptably well.

    What I am wondering whether a similar "result" is achievable using the F28069 and the QEP module. The QEP module seems to be a fairly standard peripheral across the C2000 family, at least it appears to be. The thought that using the QEP module will at least reduce the interrupt count by half ? (In comparison, to the GPIO interrupt principle; At least that basic thought)

    Does simply not connecting Index or Strobe help ?

    Thanks,

    Manu
  • 0 in reply to Manu Abraham
    TI__Guru 57255 points

    Hi Manu,

    The eQEP should work very well for you.  And yes, it should reduce the burden to your C2000 CPU.  You could just query the peripheral register when you need, instead of using interrupts at all, if that suits your system.   

    The eQEP A & B inputs are the critical two signals.  You can think of the Index & Strobe as optional signals. 


    Note: GPIO qualification can be done on any pin, whether used as a "GPIO" or as a peripheral.  Depending on how clean the output of your encoder is, enabling some amount of qualification may be beneficial for your system.


    Thank you,
    Brett