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How to check Cable diagnostics for TJA1100 PHY

Question asked by ahmed saber on Oct 29, 2019
Latest reply on Nov 11, 2019 by ahmed saber


We are using the TJA1100 as a PHY with MPC5746C.
I need to check the cable errors during the run time, either for open/short circuit between the twisted pair cables.

So I actually tried to shorten the two wires or unplug the cable from the Trcv connector and indeed I got the Link-fail counter interrupt which is fired due to the high losses/noisy channel and inside this interrupt ISR I'm gonna run the cable diagnostics, But I have some inquires


1 - If an open or short circuit happened, shall this forces the Trcv chip to go to Power down mode or it will stay in the power up mode ?


2 - Is there a specific procedure to check the cable errors " shall I write some bits in any registers " ?

according to the cabling errors section, shall I put the controller in power down mode to disable all communications ?

and then set the cable test bit, then reset the Trcv in power up as it was ?


Cable Errors


3 - I have a very weird observation: while the controller is communicating by debugging I found that the POWER_DOWN bit in the Basic control register (Register 0) equals 1, and as stated in the datasheet 1 means Trcv is in power down.


meanwhile the POWER_MODE bits(14:11) in the Extended control register (Register 17) give the value 0011 which means normal mode, so what is wrong here ?

Power down bit in the basic control Register ( Register 0)


4 - Also when I shorten the two twisted wires or unplugged them and read the External status register (Register 25)

and check on bit 7&8, I found that it didn't indicate any problem, I mean it is saying that there is no cable errors while I'm forcing a shorten or opening to the wires.



Ahmed Saber