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TL16C750E: Data bus Read Error

Roy Hsu
Genius 9300 points
Part Number: TL16C750E

Hi Team,

We tried to read back registers from the TL16C750E with an MCU but found that the rising edge ramps up slowly, causing error at the MCU side. When writing to the TL16C750E, the rising edge looks OK though. What might be the reason?

Read:

Write

Thanks!

Roy

  • 0
    TI__Guru 56040 points

    Hi Roy,

    What pins are we looking at on the o-scope? Is this one of the parallel data pins?

    -Bobby

  • 0 in reply to BOBBY
    TI__Genius 9300 points

    Hi Bobby,

    The yellow one is Chip Select (CS) and the blue one is D0.

    Roy

  • 0 in reply to Roy Hsu
    TI__Guru 56040 points

    Hi Roy,

    I think you may have uploaded the same image in your original post based on the time stamp of both pictures being 14:29. Can you provide the other picture and label which one is read and which one is write?

    Is it also possible to get the other signals on the scope (IOW/IOR)?

    My guess here is the D0 may be transitioning from an input to an output in the provided image and the fast falling edge of CS and potentially D0 trace being close to CS trace on the PCB may be causing crosstalk to temporarily push D0 low. We may not be seeing the full drop/dip on the D0 pin due to the scope's resolution/sampling rate. For a read operation, from the MCU I wouldn't expect this to cause an issue. 

    -Bobby

  • 0 in reply to BOBBY
    TI__Genius 9300 points

    Hi Bobby,

    You're right. I uploaded two identical images. Below are the correct ones:

    Read:

    Write:

    You can see DO rises up pretty slowly during read and we think that's causing some problem.

    I'll get you the waveforms of IOW and IOR shortly.

    Thanks!

    Roy

  • 0 in reply to Roy Hsu
    TI__Guru 56040 points

    Do you have a schematic you can post or maybe email me for review? I'm wondering if they have some kind of series resistor on the parallel data pins that may be causing this weird slow ramp we're seeing. 

    Thanks,

    -Bobby