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Explorer
Explorer
506 Views
Registered: ‎03-13-2014

10b8b coding K28.7 not being received, but link otherwise ok

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Hi,

My design uses a Zynq 7015 transceiver and the 10b8b coding, the code K28.5 is used for sync. I use in a legacy system so I have tested to other SERDES chips like Cypress Hotlink. The 7015 can transmit all control codes like K28.3 K28.4 including K28.7 . I can confirm that using external system. However it does not decode the K28.7 .

Any suggestions as to what is wrong, seems to decode the K28.7 as a K28.5 !!

 

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Accepted Solutions
478 Views
Registered: ‎01-08-2012

I speculate that it has been programmed to look for the "0011111" (or its inverse) comma pattern that is common to both K28.5 and K28.7.

BTW, K28.1 shares the same pattern.

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4 Replies
479 Views
Registered: ‎01-08-2012

I speculate that it has been programmed to look for the "0011111" (or its inverse) comma pattern that is common to both K28.5 and K28.7.

BTW, K28.1 shares the same pattern.

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Explorer
Explorer
464 Views
Registered: ‎03-13-2014

I since discovered the disappearing K28.7 depends on the word alignment inside the SERDES, if it is decoded in the same word as a data byte all is well. If it shares with a COMMA K28.5 then it disappears.

Decided just to avoid using this code

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Teacher
Teacher
458 Views
Registered: ‎07-09-2009

Does not the serdes reciever syncronise itself to the K28.5 pattern ?

    once its syncronised, there should not be any alignement problems

 

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Explorer
Explorer
447 Views
Registered: ‎03-13-2014

Hi John,

Yes I use K28.5 as the sync, but the interface is 16 bits, two bytes wide. If I send the code in the low byte there is a random chance that data is received in the high byte. Once the link has synced up then the byte alignment is stable. At the receive end I check signal rxchariscomma[1:0], if both are true then I don't process the bytes. What happens with K28.7 is it is decoded as a COMMA so I ignore it if the other byte is also COMMA (K28.5).

Hope that makes sense

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