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F28335 hangs at power up

Mona Gandhi
Prodigy 215 points

 

Sometimes DSP F28335 hangs up while powering up, please see below schematic for the power on reset . While  DSP hangs up  I measured the RESET signal (output of U28) by probing at pin 4of the U28 NAND gate.  It was 3.3 Volts.  I also measured the input signals to that NAND.  They were Pin 2 = 5 Volts, Pin 4 = 3.3 Volts.

Watchdog is disabled.

Please find the Power circuitry image attached.

 

 

 

  • 0
    Expert 1720 points

    Hi Mona Gandhi,

    Can you elaborate on what do you mean by a hang.

    By observing what you have mentioned that the F28335 is hanged?

    Is any software loaded in the the F28335?


    Please provide more inputs.


    Regards,

    Mohan

  • 0 in reply to B M Mohan
    Prodigy 215 points

    Yes, the software is programmed onto Flash.

    Sometimes when we power on the board the LCD screen remains blank (No character display on screen), LCD back light remains OFF. We have a LED connected to DSP which blinks at the rate of 500 ms after power up. This LED remains OFF.

    In this condition, when we do the hard reset of the DSP, it comes up normally, i.e we see the blinking of the LED as well as display on the LCD.


    Regards,

    Mona Gandhi.

  • 0 in reply to B M Mohan
    Prodigy 215 points

    Yes, the software is programmed onto Flash.

    Sometimes when we power on the board, the LCD screen remains blank (No character display on screen) and LCD back light remains OFF. We also have a LED connected to DSP which blinks at a rate of 500ms during normal operation. This LED remains OFF.

    In this condition, when we do the hard reset of the DSP, it comes up normally, i.e. we see the LED blinking and display on the LCD.

     

    Regards,

    Mona Gandhi.

  • 0 in reply to Mona Gandhi
    Expert 1720 points

    Hi Mona Gandhi,

    Thanks for the inputs, I have few more question on this.

    Since you said, the unit comes up some times and you could see the blinking LED.

    1. Do you have any while loops, in the code? If so , how do you make sure that, it will come out of the while loop.

    2. Did you try debugging by doing a single step debug?

     

    Regards,

    Mohan

  • 0 in reply to Mona Gandhi
    Expert 1070 points

    Hi,

    Can you post your power supply page as well? It would help diagnose if you put the 3.3V power supply on the scope and see if it's a clean power during start-up? 

  • 0 in reply to Leong
    Expert 1015 points

    hi mona

    i think it is hardware problem,

    you do one thing, connect oscilloscope to reset pin, and check for power on reset

    it means reset pin should low, till specified time for total hardware reset.

    regards

    nikhil

  • 0 in reply to nikhil n mane
    Expert 1150 points

    Hi

    I have a same problem with one difference: DSP always starts correctly if it is connected to the CCS with JTAG.

    When it is disconnected and hangs I can not recover it even with a hardware reset (connecting reset pin to GND).

    I used TPS767D301PWP to provide power and reset signal to DSP.

     

     

     

  • 0 in reply to Roman Ermakov
    TI__Guru* 86400 points

    Roman,

    From your description do you have proper external pulldown on TRSTn and pullups on EMU0/EMU1?  DS recommends 2.2k down and up respectively to keep the device out of test modes during operation.  This could explain why everything is working with emulator pod connected. 

     

    Best,

    Matthew

  • 0 in reply to MatthewPate
    Expert 1150 points

     Hi Matthew,

    Thank you for your answer.

    I had pullup on TRST instead of pulldown. After fixing it everything looks OK.

    I have observed one strangeness:

    if I have powered  my device with XDS510USB JTAG connected but without CCS loaded on the computer then my devise starts OK, but

    if I have powered it with XDS510PP JTAG connected without CCS loaded then it hangs.

    This  strangeness doesn't matter for my design.

     

    Regards,

    Roman.

     

     

     

     

  • 0 in reply to Roman Ermakov
    TI__Guru* 86400 points
    Roman, Glad it is working, the difference in emulators could be at play; one may not have a PD on TRSTn locally and one may. This would hurt/help your app when you had the PU on TRSTn. The other problem with this is that certain test modes are latched when TRSTn has rising edge, this is dictated by the EMU0/1 pins and is why we recommend PD on those to get into a defined state. Not sure what was on these pins on your board; but certainly haveing the test chain not held in reset would have been the problem. Best, Matthew