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DS92LX2121 I2C Pass Through

Timo Ketola
Prodigy 20 points
Other Parts Discussed in Thread: DS92LX2121, DS92LX2122

Dear all,

I'm designing with the DS92LX2121 / DS92LX2122 serializer / deserializer pair. I'm using them in display mode and on the display end I have two I2C slave chips. The system is basically working. When I put intended remote slave ID into the SLAVE_DEV_ID register in serializer, I can communicate with the remote slave. But, because I have two remote slaves, I have to rewrite the SLAVE_DEV_ID every time I want to communicate with the other chip.

I thought that the I2C pass-through mode would let me communicate with any remote slave without first writing SLAVE_DEV_ID register. But when I tried that, I couldn't communicate at all with the remote slaves.

I find it very hard to understand the 'I2C PASS THROUGH' paragraph in the datasheet.

My question is: Did I completely misunderstood the function of pass-through mode or should I look harder for a bug in my code?

--

Timo

DS92LX2121

  • 0
    TI__Expert 7395 points

    Hi Timo,

    The pass-through mode is fairly basic function; it either enables or disables I2C traffic to the remote device on the Deserializer I2C bus. In display mode, there is only one register available for the remote slave. In order to communication with different peripherals on the remote bus, you will need to reprogram the register with the target device address. 

    Dac Tran

    SVA / APPS

  • 0 in reply to Dac Tran
    Prodigy 20 points

    Thanks for your answer. What you are saying makes perfect sense. The datasheet, OTOH and IMHO, is highly misleading. The pass-through mode is almost completely explained in the paragraph "DISPLAY (or CAMERA) MODE OPERATION" and then "I2C PASS THROUGH" continues: "I2C pass-through provides an alternative means to independently address slave devices." If I now understand correctly, there is no alternative means. There is only one means to address one remote slave device and that means can be enabled or disabled with pass-through bit.