CCS/TMS320F2806: TMS320F28069M XRS Pin self resetting sometimes

Part Number:TMS320F2806

Tool/software: Code Composer Studio

Hello,

We have a strange behaviour on the XRS pin. After power up our device, XRS pin goes sometimes low after 39.8ms for about 54us.

This happens not every time only sometimes. We also dont have this behaviour on all of our devices, only with a few devices.

The duration of the XRS pin low (54us) seems like the watchdog occurred, but watchdog is disabled at initialization of cpu.

I'm also wondering, why the XRS is going low after 39.8ms. If it was a watchdog problem, the XRS pin should go low after 13.11ms.

We are using internal oscillator (10MHz).

Attached is the measured XRS pin (yellow) and power supply 3.3V (red). So the power supply is stable all time.

What could cause this reset of XRS pin?

Thanks for helping.

Regards,

Dani