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DS250DF230: Issue with CDR lock and configuration for 6.375Gbps

Roey Tal
Prodigy 165 points

Part Number: DS250DF230

Hello Team 

i have a question regarding the 

"DS250DF230EVM: PRBS Configuration at 6.375Gbps"  post i sent on augost 2025

in you reply you recommended to program registers

0x60 C0

0x61 BF

etc

i could get lock indication with this parameters however using the calculator from slnu128 it seems to be wrong

 from the slnu128 i get that the expected values are

 0x60 E0

0x61 9F (including bit 7)

 can you explain your recommendation?

 With your recommendation for programming i see in the GUI eye diagram window the value of 6.44Gbps in the Datarate and not 6.375gbps

Could it be that it looks for this value (6.44gbps)because it is in the edge of range when i set the vco divider to 4 and actually the lock is achieved only by the proximity of my bit rate (6.375gbps) to 6.44gbps

 please help with understanding the correct configuration

regards

 Roey

  • 0
    TI__Expert 8510 points

    Hi Roey,

    I will look into this and get back to you as soon as possible.

    Best regards,

    Greg

  • 0
    TI__Expert 8510 points

    Hi Roey,

    The SNLU182 document currently only has the procedures listed for calculating 0x60 and 0x61 for div-1 and div-2 subrates. Since 6.375Gbps is a div-4 subrate, the register values can be determined with (16 * 25E6) used in the formula instead of (64 * 25E6). You can find these same calculated register values of 0xC0 and 0xBF if you use 25.5Gbps in the formula for data rates greater than 13E9. Regarding the 6.44Gbps value noticed in the GUI, I can check on my end and see if I also see this. 

    Best regards,

    Greg