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Original question:

SN65DSI83: I2C Communication not working

SN65DSI83: I2C not communicating - EN held HIGH, REFCLK not used

Andy Hall24
Prodigy 120 points
Part Number: SN65DSI83

We have a SN65DSI83 on our PCB, and are attempting to communicate via I2C.

The address pin is pulled high (to 1.8V) and the enable pin is also tied high (to 1.8V). But we get no response from the IC.

We have plugged into the development board, and can communicate withe the SN65DSI83 on that, so we must be doing something wrong with the wiring of the SN65DIS83 on out PCB.

The REFCLK line is pulled to 0V via a 10k resistor, the I2C lines are pulled up via 4k7 resistors. The 1.8V and the 1.1V rails are both up and stable. Yet the SN65DIS83 is still not responding.

I tried this on one PCB, and pulled the enable pin to 3.3V, so suspect we've damaged the SN65DIS83 on that board. But have tried it on a couple of others, which have the enabled pin pulled to 1.8V.

  • 0
    TI__Mastermind 35130 points
    Hi Andy,

    Have you tried changing the slave address? When ADDR is high the slave address should be 0x2D. Please also review the i2c programming procedure on page 21 and 22 of the datasheet.

    Regards,
    I.K.
  • 0 in reply to Ikechukwu Anyiam
    Prodigy 120 points
    I have tried, checked and re-tried changing the slave address. The I2C programming procedure on the datasheet has also been followed to the letter.
  • 0
    Prodigy 120 points
    I've delved deeper into what I've got, and it appears that the EN pin is pulled low by the IC, rather than pulled up to enable itself.

    I cannot see any method by which the IC can pull its own enable pin low. As far as I can read in the datasheet (page 15) the IC pulls the EN pin up to VCC via a 200k resistor.

    What can cause the IC to pull the EN pin low?
  • 0 in reply to Andy Hall24
    TI__Mastermind 35130 points
    Hi Andy,

    It shouldn't pull low by itself. Are you controlling the EN pin through a controller on your PCB? Or could there be a a solder bridge between EN and GND (ohm it out with a multimeter)?

    Regards,
    I.K.
  • 0 in reply to Ikechukwu Anyiam
    Prodigy 120 points

    The pin is brought out to a test point at the moment, and connected to an input on a micro controller. Nothing should be pulling it low, yet it is low. There is no short to GND, it can be pulled high with a 10k resistor without any issue, and reads over 300k between the test pad and GND.

    When I pull it high with a 10K, the voltage is only 1.5V, rather than the 1.8V of VCC. So it does look like something is trying to bring it low, but only the SN65DSI83 and an input to the micro controller are connected to it.

  • 0 in reply to Andy Hall24
    Prodigy 120 points
    I have now cut the trace between the uC and the SN65DSI83, and the enable pin now appears to be high. So I'm guessing the uC somehow pulled the EN line low.

    However the SN65DSI83 is still not responding to my I2C messages
  • 0 in reply to Andy Hall24
    TI__Mastermind 35130 points
    Hi Andy,

    When you cut the trace between the uC and DSI83, is the EN pin always high now before or at the same time as Vcc is high? It is critical to transition the EN input from a low level to a high level after the VCC supply has reached the minimum operating voltage.

    Regards,
    I.K.
  • 0
    Prodigy 120 points

    Slightly embarrassingly, it turns out that one of my symbols in my schematic managed to swap the pins over, so the SCLK and SDA had swapped over.

    I have now got the SN65DSI83 responding to my I2C comms. Thanks for the help guys.