OMAP-L138: OMAP-l138 TMS pin going low

vinod Naik

Part Number: OMAP-L138

Hi,

I have customized OMAP-L138 PCB, initial testing for JTAG detection is working fine. I am able run/dump the codes, with VOICE Input (Sine Wave, 2kHz, 500mVpp) to CODEC>DSP LOOPBACK>CODEC the LOOPBACK VOICE Communication. was successful.

But after some iteration of above, all of a sudden: the OMAP Processor JTAG detection is failing (i.e., TMS Pin is showing Low Impedance ~ 40ohm)

After replacement with new OMAP Processor, board starts working, the same happened multiple times

Kindly assist for possible reasons of JTAG failure (TMS pin).

Reg,

Vinod

over 5 years ago

0 Cvetolin Shulev-XID over 5 years ago

TI__Guru 65405 points

The team is notified. They will post their feedback directly here.

BR
Tsvetolin Shulev

0 Mark Mckeown over 5 years ago

TI__Mastermind 29180 points

Hi Vinod,

Can you share the schematic screen shot of the JTAG signals? Do you have a pull-up on TMS? Are internal pull resistors enabled?

http://processors.wiki.ti.com/index.php/XDS_Target_Connection_Guide#JTAG_and_nTRST_Special_Considerations_.28includes_TMS_and_TDI.29

Regards,
Mark

0 vinod Naik over 5 years ago in reply to Mark Mckeown

Intellectual 400 points

Hi,

schematic screen shot of the JTAG signals is attached( TMS pin is Pulled-up to 3.3 via 10Kohm resistor). How to enable internal pull resistors?.

Regards

Vinod

0 Mark Mckeown over 5 years ago in reply to vinod Naik

TI__Mastermind 29180 points

Hi Vinod,

Sorry for the delay. Did you debug this issue?

Your JTAG schematic screenshot did not post to the forum.

On my OMAP-L138 EVM, the measured impedance from TMS to GND is high impedance.

Sorry, it appears that the internal pull-up resistors for JTAG are not configurable (always enabled).
Refer to OMAP-L138 Datasheet Table 3-5. Reset, NMI and JTAG Terminal Functions to see the IPU/I{D pulls for the JTAG signals.

Can you check that there are no external resistors in contention with these internal pulls?

Can you probe the rails and identify any high current consumption before or after the issue occurs?
Does the issue occur when a JTAG pod is attached? What emulator? Does the issue ever occur without the JTAG attached?

Is it possible to reproduce this issue on the EVM - OMAP-L138 LCDK for instance?

Regards,
Mark

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OMAP-L138: OMAP-l138 TMS pin going low