Power-up/ Reset state of I/O pins

22 Feb 2010

When the mbed reset is held or the board is powering up the pins p5-p30 appear to pull high.

Is there a way to ensure they stay Hi-Z or pull down during this ?

If so is there a function to set this and how is it used ?


27 Feb 2010

Yeah, I also discovered this when I was using PWM for motor control. The motor would spin up every time I reset. You can safely pull them down with a resistor. It seems that when you hold the reset, the pins aren't really on, they are in some sort of high impedance state, but at a 3.3V level, which can still trigger some devices as you reset.