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TMS320F2809: EMU0 EMU1 TRST pullups, pull downs, watchdog and illegal_isr()

James Cechvala
Prodigy 40 points

Part Number: TMS320F2809

Looks like I'm having some issues with these pins.  I'm running this chip in an industrial drives type application so I would say that it is a noisy environment.  I was having a chip spontaneously reset usually after running for about 5 minutes.  Sometimes it would watchdog reset, sometimes it would go into Illegal_ISR().  Looking at the design at the moment, I don't have any pull up or pull down resistors on any of those 3 pins which is different from the datasheet recommendation on page 18.  Couple questions related to this:

  1. Can noise on these pins cause watchdog reset?
  2. Can noise on these pins cause Illegal_ISR()?
  3. Datasheet says to use pull up on EMU0 and EMU1 but it says the chip enters debug mode when EMU0 is logic high and EMU1 is logic low, so why not a pull down on EMU0 and pull up on EMU1?
  4. I don't need hardware debugging, can I use as low as a 0 ohm pull up/down?  How about 100 ohms?  I understand that I can't program like this but that doesn't matter to me.
  5. Would it be better to pull up to 5V instead of 3.3V?
  • 0
    TI__Guru 57255 points

    Hi James,

    I would highly recommend adding these resistors - especially the one on TRSTn.  There is an internal pull-down on this pin, but in noisy environments we require that customers put a relatively strong pull-up externally.  While you can directly short TRSTn to ground (or pull via a 100ohm resistor), a 2.2Kohm is very likely to be sufficient, assuming that it is appropriately placed near the C2000 device.

    I don't believe EMU0 and/or EMU1 to be as critical, but I would recommend following the datasheet's specifications.

    I suspect this is likely to be directly related to the issue you're having.


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    TI__Guru* 95315 points
    Agree with Brett that –TRST is likely the culprit. To verify this, you could short this pin to GND (or through a very low R like 100 ohms or less). Noise on –TRST could indeed make the device act weird. Another area to focus is the –XRS pin itself. Please check if it is stiff and immune from noise.
  • 0 in reply to Hareesh Janakiraman
    Prodigy 40 points

    Thanks, 100 ohm pull up on TRST gave me many hours of run time without problems when previously I would run into problems after about 15 minutes typically so I think that fixes the problem.  My programmer still manages to program too which is nice.

  • 0 in reply to James Cechvala
    TI__Guru* 95315 points

    Perhaps you meant a pull-down and not a pull-up. Please size the value of the PD resistor such that it offers the immunity you need, but at the same time does not stress the output buffer of the emulator driving the –TRST pin.