XEM6310MT GTP termination


#1

I am trying to interface an LVPECL differential signal (from a Micrel SY58012U) with the GTP of a XEM6310MT board.

It should be possible but I am seeing bit errors (probably about 2 bit errors every 50 bits). I am receiving the K characters I am transmitting from another system but with corruptions.

Coupling capacitors have been installed for all of the RX pairs but a value is not noted, I am presuming they are 100nF.

Has anyone else tried to connect LVPECL signals to the XEM6310MT board?
Do you have any suggestions for termination?


#2

Here’s an update.

I have pulled the +ve and -ve signals to ground using various values of resistor. This step appears to be necessary (results in data that is recognizable) although it doesn’t seem to matter what values are used. 47 Ohms up to 220 Ohms seemed to give similar results.

I was still getting errors until I momentarily shorted one of the differential signals coupling capacitors on the Opal Kelly board. The result is that the errors are gone, at least until I power down and back up again.

Any ideas?


#3

I am now terminating both +ve and -ve signals through 150 Ohms to ground. I have also added a series resistors of 27 Ohms.

This seems to work fine.

The problems I was facing seem to be to do with not resetting the GTP correctly. My hardware allows me to externally change the reference clock frequency, I was not waiting long enough for it to settle (when powering up) before resetting the GTP.