How to check Cable diagnostics for TJA1100 PHY

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How to check Cable diagnostics for TJA1100 PHY

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ahmedsaber
Contributor I

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 ?

Cabling errors.PNG

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.PNG

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

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3 Replies

159 Views
ahmedsaber
Contributor I

Hello bpe,

Thanks for your reply.

As mentioned in the application note:

6.5 Cable test
Cable test trigger.PNG

6.1 Link control

Link Control.PNG

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

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159 Views
ahmedsaber
Contributor I

Hello,

Any response please

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159 Views
bpe
NXP TechSupport
NXP TechSupport

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