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Original question:

CCS/EK-TM4C123GXL: Read signal from encoder does not wait for signal.

CCS/EK-TM4C123GXL: Connecting an OMRON encoder

William Herschel
Intellectual 640 points
Part Number: EK-TM4C123GXL

Tool/software: Code Composer Studio

Hello,

I am interfacing an OMRON quad encoder which produces this waveform on Phase A (and B). The voltage level varies between about 4.5 and 0 V so will it work if I attach it directly to the TM4C123GXL pins or does it need a level shifter? Thank you.

  • 0
    TI__Guru**** 190806 points

    Hi William,

      I cannot see the waveform. Can you please attach again? If your input only varies between 4.5V and 0 then it should be fine as most of the TM4C123 GPIOs are 5V tolerant except those specifically called out not 5v tolerant . The output is only 3.3V. Please be cautious that the input never exceeds the maximum allowed as defined in the datasheet electrical section. 

      

  • 0 in reply to Charles Tsai
    Intellectual 640 points

    Hello Charles,

    Thank you for your reply. Sorry I pasted the image which looked all right on my screen but obvioulsy I need to insert the file.

    My question was really whether the waveform will trigger the QEI interrupts correctly as it swings outside the 3.3V.

    Thanks again

    William

  • 0 in reply to William Herschel
    TI__Guru**** 190806 points

    Hi William,

      Yes, it will trigger QEI interrupts correctly. 

  • 0 in reply to William Herschel
    Guru 117855 points

    Greetings,

    While agreeing w/vendor's Charles should not (some) attention be directed to the 'Degree of Over-Shoot' that cap evidences?

    Our firm employs 'self-designed' & 'other-branded' commercial encoders - none exhibit such over-shoot!    And - should you 'magnify the horizontal scale' - might transient levels (peaking beyond 5V even) reveal?

    Unknown are the 'drive conditions' under which the scope cap was taken.    It should be noted that 'excessive cable/wire length' - between encoder & MCU often adds inductance - which (likely) generates (unwanted) voltage spikes - which may (in time) prove injurious to the MCU...   (especially w/the motor noise - which (also) demands management...)

  • 0 in reply to cb1_mobile
    Intellectual 640 points

    Thank you cb1_mobile for pointing out some additional considerations to consider. I may experiment to see if I can identify the reasons for the overshoot. At the moment there is nil progress because I blew up the Launch Pad and encoder by connecting the scope probe ground to a live rail so have to wait for replacements.