While installing my Red controller in the BUD NEMA box, I prepared a harness that plugged into the pins on the top of the STM32F4Discovery board for the two external pushbutton switches I mounted on the case. The NRST line for hard reset and PA0 line for the user blue button appear on one of the pair of rows of parallel pins on the top of the board.
As expected, hard reset was triggered by grounding the NRST line. However, grounding PA0 did not control the LCD display - no effect. I checked the schematic and found that the NRST line has a pull up resistor to keep the line at +5vdc when the button is open.
However, the PA0 button was wired in reverse. There was a pull down resistor on PA0 that kept the line at 0vdc when the button was open. It was necessary to bring PA0 to +5vdc to trigger the LCD and other control functions.
Therefore, GND and NRST need to go to the momentary SPST button for reset. +5vdc and PA0 need to go to the LCD control switch.
I used Greg's idea of using an internal PC audio cable to make the three connections (all in a line) to VDC, GND and NRST. I used an old portable phone battery connector and wire to connect to the PA0 line, which is a few pins down from the other three signals on the pins. I cut the black wire off the repurposed battery connector to avoid bringing the adjacent signal to PA0 up to switches. I thought this might cause noise pickup on that line.
Regards,
Don