TDES954: V3Link: PASS toggling in and out

Luis Villaran

Part Number: TDES954
Other Parts Discussed in Thread: TSER953,

I have a custom board with a TSER953 and a camera sensor on it. When I hook it up to a deserializer board (have tried both an EVM and a custom board with TDES954 on it) I am getting a PASS signal that is toggling in and out very quickly (10s of ns -- average frequency of about 6.6 MHz). The LOCK signal is solid.

More details on the setup:

- Connected through STP wire of about 3 feet (not long)

- The custom deserializer board has been tested with another custom serializer board and works fine there, so that is a (somewhat) trusted entity

- I have tried multiple grounding schemes and converting both sides to coax to no avail

- Cannot share schematics for IP reasons, but would be happy to do so in a private message if necessary

Is this something that has been seen before? What are some debugging steps I can try to get to the bottom of why this is happening?

over 2 years ago

0 Nicholas Darash over 2 years ago

TI__Mastermind 18755 points

Hi ,

We can go over schematics if we need to but I think we can try some other things first. What video data is being sent over the link? Is the TESER953 connected to an image sensor or are you using PATGEN?

I think a register dump may be useful as well.

Regards,

Nick

0 Luis Villaran over 2 years ago in reply to Nicholas Darash

Prodigy 80 points

Thanks, Nick. The TSER953 is connected to an OV2740 image sensor so we are not using PATGEN, I was under the impression that we needed to get a solid PASS / LOCK signal before the image sensor connection becomes relevant -- is that not true?

I can't seem to attach the .nrd here, so could you provide me an email I can send that to?

0 Nicholas Darash over 2 years ago in reply to Luis Villaran

TI__Mastermind 18755 points

Hello,

The LOCK signal just means that the deserializer can communicate to the serializer however the PASS signal has some additional conditions which can be set in register 0x7D. Can you read back registers 0x4D, 0x4E, and 0x7D.

Regards,

Nick

0 Luis Villaran over 2 years ago in reply to Nicholas Darash

Prodigy 80 points

Ok, understood. This is what I got:

0x4D = 0x7

0x4E = read both 0xCD and 0xC9 but most of the time 0xCD

0x7D = 0x00

0 Luis Villaran over 2 years ago in reply to Luis Villaran

Prodigy 80 points

0x4D also sometimes reads 0x17

0 Nicholas Darash over 2 years ago in reply to Luis Villaran

TI__Mastermind 18755 points

Hi Luis,

It seems like some errors are occurring on the link which may be part of the problem. Are you able to run the map script to test the quality of the link?

https://www.ti.com/lit/an/snla301/snla301.pdf

https://www.ti.com/lit/ug/snlu243/snlu243.pdf

Regards,

Nick

0 Luis Villaran over 2 years ago in reply to Nicholas Darash

Prodigy 80 points

Hi Nick,

I was able to run, but it didn't look great -- essentially every EQ / SP combo was red. What could cause something like that? I've triple checked my connections and they all seem okay to me. The FPD link is running through a <= 1 ft coax, not long at all. Are there other things to check?

luis

0 Nicholas Darash over 2 years ago in reply to Luis Villaran

TI__Mastermind 18755 points

Hi Luis,

Sometimes the very short cables can actually have worse return loss than the longer cable which could lead to issues. Is it possible to evaluate the return loss and insertion loss of the overall channel?

Regards,

Nick

0 Luis Villaran over 2 years ago in reply to Nicholas Darash

Prodigy 80 points

Hi Nick,

Insertion loss for Fc, 2 x Fc, and 3 x Fc and the return loss for Fc, 2 x Fc, and 3x Fc (in that order) are given for one of my coaxial cables below.

However, I have tried multiple coax cables at differing lengths and they all result in the same oscillation on the PASS line at about the same 6.5 - 6.6 MHz frequency, so to me it feels like there may be something independent of the cable going on...?

Thanks,

luis

0 Nicholas Darash over 2 years ago in reply to Luis Villaran

TI__Mastermind 18755 points

Hi Luis,

Can you share the registers?

Regards,

Nick

+1 Luis Villaran over 2 years ago in reply to Nicholas Darash

Prodigy 80 points

Hi Nick,

Turns out the schematics I was given did not match the BOM that was used, so the resistor values for the MODE and IDX looked good on paper, but we're all off on our boards. After fixing them, I now have a consistent PASS and LOCK signals. Still trying to figure out the correct configuration, but at least this mystery is solved.

Thanks,

luis

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TDES954: V3Link: PASS toggling in and out