DP83822I: 100BASE-TX Duty Cycle Distortion Compliance Test

Hi Patrick,

Please see register 0x0027 in the datasheet.

Thanks,

David

Hi David,

Can you please be a bit more specific about how to set register 0x0027 for a  100BASE-TX "01010101 NRZ" pattern.

Regards,
Patrick

Hi Patrick,

Please see section 3.3.8 of the following app note: SNLA266

Thanks,

David

Hi Patrick,

Please see this snippet from a Tektronix app note:

To run the Duty Cycle Distortion test, you should not need to explicitly generate a 0-1-0-1 pattern. Rather, the oscilloscope will find the 0-1-0-1 pattern within the test pattern which SNLA266 shows how to generate. 

I should not have mentioned it, but register 0x27 can be used to explicitly generate a 0-1-0-1 pattern as described in detail here, but you should not need to do this:

Thanks,

David

Hi David,

When I set register 0x0027 to 0x0001 and register 0x0428 to 0x0010 (single 0 after a 1)  I get the following signal at the transmitter:

But I expect to get this:

Regards,
Patrick

Hi Patrick,

What is the reason for wanting to do this? There is no need to set this to run the compliance test.

Before writing to register 0x0027 and 0x0428, have you forced the speed to 100Mbps in the Basic Mode Control Register? You can do this by writing 0x2100 to register 0x0000.

Thanks,

David

David,

Yes, speed has been set to 100Mbps in Basic Control Register.

Regards,
Patrick

Hi Patrick,

Please try running the compliance test following the direction of SNLA266 without writing to register 0x0027 or 0x0428. Let me know the results. 

In parallel, please send me a screenshot of reading register 0x0000, 0x0027 and 0x0428 after writing to them to ensure the write was performed correctly.

Thanks,

David

Hi Patrick,

The normal implementation is to use a continuous MDC clock. You can add an additional read at the end of your write sequence to fix this issue, then. Glad to hear the expected pattern is showing now. Is there anything further I can help with?

Thanks,

David

Hi David,

It would help to have this mentioned in the datasheet of the DP83822I. Especially if one reads the following in the datasheet:

If this is not known one could try for ever to generate a needed pattern.

For the time beeing no further help is needed.

Thanks and best regards,
Patrick