How to check Cable diagnostics for TJA1100 PHY

[ahmedsaber]

Hello,

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 ?

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 ?

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.

Thanks
Ahmed Saber

[ahmedsaber]

Hello bpe,

Thanks for your reply.

As mentioned in the application note:

6.5 Cable test

6.1 Link control

So I'm little confused, how PHY must be in normal mode and required to disable the link control, while disabling the link control will force a transition to standby mode.

then PHY is not in the normal mode yet.

Also: what about points 3 & 4 in the original question,  do you have any explanation or suggestion what is wrong ?

Could you please clarify the answers for each questions in their positions

Thanks

Ahmed Saber

[ahmedsaber]

Hello,

Any response please

[bpe]

You cannot get cable errors during the normal operation, you can only
see the link status change. Cable errors are result of cable diagnostics
which is _not_ the normal mode and requires LINK_CONTROL = 0.
Refer to AN12088 Section 5.2.2 for Link Status,
to Section 6.1 for the function of LINK_CONTROL and to Sections 6.4
and 6.5 for test modes. The document can be found on the public
SJA1100 Product Page:

https://www.nxp.com/docs/en/application-note/AN12088.pdf