DP83869HM: Strapping issues

kathy jacques

Part Number: DP83869HM

Hello,

Can you provide any details on when the strap signals are sampled?

I had assumed they would be sampled on the rising edge of RESET_N, but that doesn't appear to be the case.

I have the OPMODE_0 strap (JTAG_TDO) driven with a buffer that uses the RESET_N as the enable to the gate. The thought was that we would stop driving it prior to the DP83869HM driving the TDO output, but the strapping is not being sampled correctly. I have verified the buffer is behaving as expected.

Looking at the datasheet, I do not see any timing information regarding when these signals are sampled.

Thanks!

kathy

over 3 years ago

0 Gokul Koraganji over 3 years ago

TI__Mastermind 19250 points

Hi Kathy,

Straps are sampled a few us after the rising edge of RESET_N. Since the buffer is being gated by RESET_N, the buffer is driving JTAG_TDO immediately after RESET_N posedge. Can you please try gating the buffer for 30us after RESET_N is released?

--
Regards,
Gokul.

0 kathy jacques over 3 years ago in reply to Gokul Koraganji

Prodigy 20 points

Not easily. But I might see what I can do as an experiement.

i just wanted to verify that my understanding of the problem made sense based on how the part works, and it sounds like it does. The buffer has a propagation delay in the <10ns range, which would certainly mean we are not driving the signal a few us later when they are sampled.

In the long run, I might just remove the buffers, and strap with resistors. I have verified that this works in the lab.

Thank you.

0 Gokul Koraganji over 3 years ago in reply to kathy jacques

TI__Mastermind 19250 points

Hi Kathy,

Thanks for the update. Please keep me posted.

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Regards,
Gokul.

0 Gokul Koraganji over 3 years ago in reply to Gokul Koraganji

TI__Mastermind 19250 points

Hi Kathy,

Were you able to solve the issue?

--
Regards,
Gokul.

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DP83869HM: Strapping issues