Question about NRST pin on STM32F051

mvonahnen · ‎2015-01-28

Posted on January 29, 2015 at 02:12

We have a design were we are periodically going into stop mode, waking up on a RTC interrupt, running some code, then going back to stop mode. Every time the processor wakes up, the NRST pin goes low for approximately low for 25 usec. The pin is not being driven externally, so it appears to be responding to an internal reset.

What would cause this behavior?

mvonahnen · ‎2015-01-29

Posted on January 29, 2015 at 18:15

I also looked at the Option bytes, which could cause this behavior and I found that they have not changed from the defaults: 0x1FFFF800 = 0x00FF55AA, 0x1FFFF804 = 0x00FF00FF, 0x1FFFF808 = 0x00FF00FF.

Tesla DeLorean · ‎2015-01-29

Posted on January 29, 2015 at 18:52

The pin is bidirectional, and if it's like any of the other STM32 there at least a dozen signals that will generate a reset.

Is the device actually going into STANDBY?

Is the pin pulled high externally, by a supply that does not turn off?

Is the supply browning out? ie causing the BOR or POR to fire, check analogue supply

What does the reset register attribute as the cause of the reset?

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waclawek.jan · ‎2015-01-29

Posted on January 29, 2015 at 19:11

Are you sure you use Stop mode and not Standby mode?

[edit] overlooked that Clive asked the same above sorry [/edit]

Is register content (e.g. RCC registers) retained?

Any watchdog used?

JW