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SN65HVD251: signal integrity on TX and RX

Abderrezak HADJI
Prodigy 40 points
Part Number: SN65HVD251

Hi, 

I am using the SN65HVD251 CAN-transceiver in a critical application. I have to operate some tests to validate my architecture. My architecture, after a time out, can redirect TXD and RXD on a second independent CAN-bus : if one bus is off the second is used.

One of my tests consist to pull up CAN-H and/or CAN-L to Vcc then track the TXD and RXD signals, this test fail by affecting TXD and RXD (pulling down CAN-H and/or CAN-L to Vcc succeed)

So, I am not able to redirect a correct data (TXD and RXD) to the second CAN-bus. I am scratching my head to understand how pulling up CAN-H and/or CAN-L to Vcc can affect TXD and RXD signals? Is there a way to fix this?

Regards,

Abderrezak.

  • 0
    TI__Guru 62910 points
    Hi Abderrezak,

    I'm not sure I totally understand the problem you are seeing. In general, pulling CANH to ground or CANL to VCC should cause communication failures (RXD signal no longer toggling), while pulling CANH to VCC or CANL to ground may not. Is this in line with the results you are getting?

    The reason the second case may not result in errors is that the differential voltage present on the bus between CANH and CANL is likely still large enough during "dominant" states and small enough during "recessive" states to be properly resolved by a CAN receiver.

    I hope this helps, and please let me know if I've misinterpreted your post or can help provide any more clarity.

    Regards,
    Max
  • 0
    Prodigy 10 points

    Hi,

    I hope that u hav solved all ur prblems nd it remains juste that one.

    Regards,

    I.CH