STM32F4 NRST pin - two questions

[mehmet.karakaya]

Posted on January 21, 2013 at 22:08

hello forum,

I have an industial controller board where I need a reset signal for turning off output relays when the STM32F4 is resetted by either by the 100nF cap at the NRST pin when booting or by the watchdog timer my question can I load the NRST pin with a 74LS input ? does the NRST pin goes to low when watchdog timer resets the STMF4 ? thank you #stm32f4-reset

[Tesla DeLorean]

Posted on January 21, 2013 at 22:32

You're not going to be able to get it to 5V (not tolerant), it will be pulled up to 3 or 3.3V whatever your supply to the STM32 is. I don't think it would have a problem driving an LS series schmitt trigger, there might however be other 74 series parts better suited.

It gets clamped low via an open-collector driver which is thresholding the supply voltages. My recollection is that the IWDG doesn't drive NRST low, but it would only take a couple of minutes for you to verify off one of the firmware library examples. If it doesn't consider an external watchdog solution that drives NRST low, although you won't be able to determine that as a reset cause in the status registers.