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peter
peter
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I am trying to connect New Haven Display NHD-5.0-800480Tf-ATXL#CTP touchscreen with i2c touchpanel to igepv2 using i2c3 on pins JA41 27, 28. I built a separate interface board using TXS0102DCUR translator with 4.7k pullup resistors and 100k OE resistor wired exactly as per IGEP Berlin and IGEPv2 EDID I2C interface on ISEE schematics. But I am getting very strange results

Using i2cdetect -r 3 I find
I2c3 on HDMI works fine when connected to a screen giving 37,3a and 70 addresses
I2c3 does not find touchscreen when HDMI detached and pins 27,28 attached to interface board as above.

I used an oscilloscope to test the i2c3 signals on pins 27,28 - no device attached but issuing i2cdetect -r 3 commands to send signals.
post-TXS0102 I get a SCL signal 3.3v but no SDA signal via i2cdetect -r 3 (SDA stays at 3.3v)

pre-TXS0102 I get SCL 1.8V signal and SDA=0V via i2cdetect -r 3


My connector board schematic is attached. Is there anything obviously wrong? Am I missing something? Does HDMI need to be shut down somehow in software?
< see attachment>
Attachments:

Accepted Answer

Tuesday, March 08 2016, 12:03 PM - #permalink
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Hi peter,

In idle state, I2C3_SDA must be pulled high (1V8). Do you have the same behaviour, I2C3_SDA pulled low, when your expansion board is plugged and unplugged from IGEPv2?

Cheers!

PD: In your hardware design, resistors R3 and R4 are not necessary, because IGEPv2 has pullup resistors into I2C3 1V8 bus
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Responses (4)
  • Accepted Answer

    peter
    peter
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    Friday, March 04 2016, 12:05 PM - #permalink
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    My apologies - here are the oscilloscope files in pdf format (bmp didn't upload).

    Peter
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  • Accepted Answer

    peter
    peter
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    Wednesday, March 09 2016, 06:54 PM - #permalink
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    Thanks for the response. Yes, the I2C3_SDA is low when my expansion board is not connected. With your response, I can think of only 3 possible reasons.
    1. The ribbon cable which I used to connect the JA41 header to the expansion board (and the oscilloscope) is faulty.
    2. My soldering of the JA42 header to the IGEPv2 board is faulty.
    3. I somehow fried something in the IGEPv2 board to cause this behaviour.

    I will experiment and post my results. Thanks for the hint on my connector board design. I will fix that as well.

    Peter
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  • Accepted Answer

    peter
    peter
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    Saturday, March 19 2016, 06:36 PM - #permalink
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    Yes - it was a faulty Samtec ribbon cable - pin 28 didn't connect through. Attached is what I get now with a new cable. Thanks for you guy's help.
    Attachments:
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  • Accepted Answer

    Monday, March 21 2016, 10:47 AM - #permalink
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    :)
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