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Interfacing incremental position sensor to F28035

Sandhya Jetti
Intellectual 535 points

Hello all,

I am using F28035 expeirmenter;s kit and trying to interface an incremental encoder. The three inputs ChA, ChB and Index are 2.5V max square wave and draw only 25uA after signal conditioning. I have put jumpers to GPIO 20, 21 and 23 respectively, but they are forced to high on that pins even when the motor is spinning. When I disconnect the jumpers I can see the signals good. 

I can post part of my code how I configured the inputs and the QEP peripheral. 

Any ideas why it would be forced to high and not read any values?

Thanks in advance

sandhya

  • 0
    TI__Guru 57255 points

    Sandhya,

    What is the output of the incremental encoder?  Common collector?  Push-pull?  Can you tell via the encoder datasheet?

    My guess is that the forcing of the encoder signals is due to internal pullups which are enabled by default on many of the GPIO pins.  They can be disabled by software however.  Refer to the GPxPUD register in the F2803x System Control and Interrupts user's guide.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Intellectual 535 points

    Thank you very much Brett,

    I can read the inputs on the pins when I disabled the pull ups. I could not find what the output of the incremental encoder is, I am using ENC-A3I from anaheim automation

    http://www.anaheimautomation.com/products/encoder/incremental-rotary-item.php?sID=352&serID=4&pt=i&tID=1054&cID=422

    It will be great If you can help me understand! 

    Thanks

    Sandhya

  • 0 in reply to Sandhya Jetti
    TI__Guru 57255 points

    Sandhya,

    From a quick glance, it looks like the encoder can drive its output low and high.  However, you may want to look into this more to be certain.

    The C2000 device internal pull-up's "resistance" is specified as the amount of current draw in the datasheet.  This is because it is an active circuit not a resistance.  Even though it isn't fully accurate, you can approximate resistance from this number (from memory it is around 5K). 

    I am surprised that ~5Kohms would pull up your signal, but perhaps your signal conditioning circuitry is playing a role too.


    Thank you,
    Brett