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TMDS181: SWAP function and I2C

Nicholas Carley
Genius 9945 points
Part Number: TMDS181

I have a question about the SWAP/POL pin on the device.

The SWAP/POL pin is tied to GND through a 65K resistor.
The I2C_EN/PIN is tied to VCC through a 65K resistor.

The receiver lanes are swapped for ease of routing and according to the datasheet (see Table 2), the UNSWAP can be accomplished by the pin or by writing to a register through I2C.

I am relying on the SWAP/POL pin to automatically unswap the lanes on power up, before our I2C controller is ready.
That is not happening. The swap only works after the register is written.

Does I2C take precedence over the pin since the I2C_EN/PIN is tied to VCC ?

I am confused by the “NOTE” in register description (see Table 6, 0x09h), that the field is loaded from the SWAP/POL pin. In that case, does it a load a LO on power up and disable the swap?

Thanks,
Nick

  • 0
    TI__Guru**** 177466 points

    Nick

    TMDS181 supports pin-strap control mode and I2C control mode.

    When I2C_EN is High, TMDS181 is in I2C Control Mode and LANE_SWAP can only be configured through the I2C register address 0x09h, bit 7. When I2C_EN is Low; TMDS181 is in pin strap mode and LANE_SWAP is configured through the SWAP/POL pin.

    The note simply states that when I2C_EN is low, write to register 0x09h bit 7 has no effect on the lane swap.

    Thanks

    David