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TMS320F2809: XRS goes Low

Steven MacDonald
Intellectual 450 points
Part Number: TMS320F2809

We are cold soaking a ups to -10C. The processor will start up breiefly then the xrs pin goes low for a few hundred milliseconds then high for 1.5 seconds then low then repeat. The input supplies look good during this time so they have been ruled out. there is a 10k pullup on the xrs pin with a 1n cap to gnd. We do not have the watchdog timer enabled in the firmware so we fail to see how the DSP is able to pull the xrs pin low. Once we let the unit warm up a few degrees it does start normally.

Can the xrs pin be pulled low by other means. As I said the watchdog timer is not enabled.

Thanks!

  • 0
    TI__Mastermind 27200 points
    Steven,

    You are right to think of the watchdog.

    The watchdog is enabled by default. If you do not want to use it you have to manually disable it in the code. I guess you are doing that early in initialization, but take a look at where it's happening. In TI example code there's usually an "InitSysCtrl" function, just after main(), and the first line in that disables the watchdog before waiting for the PLL to lock. I'm wondering if you do the PLL lock with the watchdog active and it's taking longer at the lower temperature?

    Do you know if it's repeatable, or do you just have one unit with this behaviour?

    Regards,

    Richard