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DS90CR486 DC balance mode

user4682316
Prodigy 20 points
Other Parts Discussed in Thread: DS90CR486, DS90CR485

Hi,

we bought a DS90CR486 133MHz 48-bit Deseriallizer and make a PCB board to measure it.

We want our deseriallizer works on DC balance mode.

So we design our BAL pin tied to high, CON1 tied to high and DESKEW tied to high too.

But after measurement, it seems like the deseriallizer works on disable dc balance mode.

Can anyone give us any suggestion or telling us which pin may also effect the deseriallizer in DC balance mode.

Thank you

  • 0
    TI__Mastermind 29655 points
    Hi,

    The DS90CR486 DC balancing only works if the transmitter (presumably the DS90CR485) is also in DC-balance mode. Otherwise, the serialized bit mapping into the DS90CR486 will not match as expected.

    Please provide a schematic of Tx and Rx if possible.

    Regards,

    Michael
  • 0 in reply to Michael Lu (Santa Clara)
    Prodigy 20 points

    Hi,

    Thanks for your replying.

    The file below is our testkey schematic.

    So if we only use the pattern generator to test the deseriallizer , it won't work on the DC balance even if we tie BAL pin to high, CON1 to high and DESKEW tied to high too ?

    Regards,

    Chien-Cheng Wang

    deseriallizer .pdf

  • 0 in reply to user4682316
    TI__Mastermind 29655 points
    Hi Chien-Cheng,

    Thank you for the schematic.

    After reviewing it, I do not see anything wrong with the connections so far. Thanks for letting me know what you are connecting to our device as a transmitter. My thought is that you will not be able to use the deserializer with DC Balance Mode on if you are hooking up a pattern generator at the input. The reason why is because the final bit in each 7-bit serial sequence is a "DC Balance" bit that indicates to the deserializer to invert or non-invert the other bits in that clock period. Since your transmitter is a pattern generator and is not using this final bit per clock period to invert/non-invert the previous 6 bits of data, the DS90CR486 will be inverting or non-inverting each clock period's 6 bits of data depending on whether the 7th bit is a 0 (non-invert) or 1 (invert). This will lead the error analyzer after the DS90CR486 to interpret the DS90CR486 outputs to be incorrect, depending on whether the polarity of the output bits are inverted, and this issue will happen depending on whether that final bit is a 0 or 1.

    Unless the transmitter is able to support this DC Balance Mode, DC Balance Mode for the DS90CR486 should be disabled.

    Michael