P3: LED Matrix (Column 1)

P3 is wired to Column 1 of the onboard 5x5 pixel LED matrix on the BBC micro:bit.

While the LED matrix is 5x5 (25) pixels, there are 9 columns and 3 rows. Columns 8 and 9 drive only two LEDs each.

While you may use this pin for other purposes, you must take into account that it is wired to LEDs and their associated resistors.