TMS320F28375D: Unable to drive TRST pin high

Pratham Sarvaiya

Part Number: TMS320F28375D
Other Parts Discussed in Thread: LP-XDS110

Tool/software:

Hello,

I am using the TMS320F28375DPZPS on a custom designed board. I am unable to program the device using TI's XD JTAG debugger. After plenty of debugging, I realise I am unable to drive the TRST pin high on the microcontroller in order to connect to the device via JTAG

My findings:
- I had initially added a 10k pulldown resistor to the TRST pin.
- On CCS, I am unable to connect to the device (the JTAG connection fails ) - I am able to program other C200 platforms so I know it may not be a software issue

- The TRST pin is normally at 0.2V with the pulldown resistor. The debugger is unable to drive the TRST pin high, so I tried shorting the TRST pin to 3V3 (with and without the pulldown) - This brings down the entire 3v3 rail to 0.2V.

- I then tried adding a 10k pull up resistor the TRST line (and removed the pulldown) - this makes the TRST pin around 0.4V

- Without any resistor connected to the TRST pin, I measure roughly 300k resistance between TRST pin and ground, as well as roughly 300k resistance between TRST pin and 3V3.
- The board and Microntroller seem to be powered and clocked correctly because I can see the watchdog continously triggerred ( this is a new unprogrammed device)

- The debugger I am using seems to be running fine as I see activity on the clock and data lines coming from the debugger.

Any advice on next steps ? I am unable to connect to the TMS320F28375DPZPS.

Thanks.

8 months ago

0 Benjamin Collier 8 months ago

TI__Mastermind 36526 points

Hi,

Which debug probe are you using? The debug probe should hold TRST high whenever it is communicating with the MCU. It sounds like the debug probe is pulling it low.

Could you try disconnecting the debug probe from TRST, while pulling TRST high? Can you connect in this case?

Do you have a different debug probe that you can try?

Thanks,

Ben Collier

0 Pratham Sarvaiya 8 months ago in reply to Benjamin Collier

Prodigy 10 points

Hi,

With the debug probe disconnected, I tried pulling TRST high to 3V3 directly. The voltage at the TRST reads 0.4V. Same result if it is pulled high through a 10k resistor. Still unable to connect

0 Benjamin Collier 8 months ago in reply to Pratham Sarvaiya

TI__Mastermind 36526 points

Hi,

Pratham Sarvaiya said:
With the debug probe disconnected, I tried pulling TRST high to 3V3 directly. The voltage at the TRST reads 0.4V.

For this to be true, TRST must be sinking a lot of current.

This sounds like the MCU is damaged. Can you try swapping the MCU?

Thanks,

Ben Collier

0 Pratham Sarvaiya 8 months ago in reply to Benjamin Collier

Prodigy 10 points

Hi,

I swapped the MCU and was still unable to connect.
I am using the LP-XDS110 debugger.

Since the MCU is still able to watchdog reset continously, it makes me think that the MCU is not damaged.

Thanks.

0 Benjamin Collier 8 months ago in reply to Pratham Sarvaiya

TI__Mastermind 36526 points

Please share the schematic for your TRST circuit. Something simple here is not right, you should be able to pull the TRST pin high.

0 Pratham Sarvaiya 8 months ago in reply to Benjamin Collier

Prodigy 10 points

I tested with R23 as 2.2k as well as 10k and did not see any difference. XRS is pulled high.

0 Benjamin Collier 8 months ago in reply to Pratham Sarvaiya

TI__Mastermind 36526 points

Hi,

Are you saying that even with the debug probe connected, you cannot force MCU TRST device pin to be high?

How much current is going to the pin when you try to force it high? You should be able to force it high when the debug probe is not connected.

Once you force it high, you should be able to connect the other JTAG pins and program the device.

Best Regards,

Ben Collier

C2000™︎ microcontrollers

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TMS320F28375D: Unable to drive TRST pin high