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TMS320F28335: JTAG and EMU Pins

user1347906
Prodigy 110 points

Part Number: TMS320F28335

I am using TMS320F28335 for an inverter.
The microcontroller goes into a reset state when the PWM output is turned on.
The current schematic of the JTAG line is shown below.

I was suspicious of the JTAG line and referred to the 3.3.2 Important Careabout With JTAG and EMU Pins section of the following guidelines

www.ti.com/.../spraas1d.pdf 28335%253FkeyMatch%253DTMS320F28335
EMU0,EMU1=4.7Kohm->2.2Kohm
TRST=2.2Kohm->1.1Kohm
Is this reasonable?
(How low can the resistance go?)

I am also considering adding 0.01microF capacitors to EMU0, EMU1, and TRST.

If I deal with either changing the resistor value or adding a pass-controller, which would be more effective?

  • +1
    TI__Mastermind 36526 points

    Hi,

    Are you able to watch your JTAG signals with an oscilloscope to see the noise? 

    We do not give any specific guidance on the minimum or maximum value of the pulldown resistor on TRST, since this will depend on your debug probe. You will have to see if it is still possible to program your device with the stronger pull down resistor. If you are ok with not being able to program the device any more, you could even tie TRST to ground with a 0 ohm resistor.

    I have not seen anyone use a low-pass filter on their JTAG signals. It might be ok on TRST, but I am not sure. 

    Also, excessive noise could cause problems other than the JTAG problems you are experiencing. What does the circuit on your XRS pin look like?

    Best Regards,

    Ben Collier