The following byte holds the result of reading the keyboard and joystick, as done by the interrupt routine at $39C7. It holds $00 if there was no input, the ASCII code of the key pressed (if any), or one of the following values if the joystick was moved:

Value	Meaning
$D1	Up ('Q' with bit 7 set)
$C1	Down ('A' with bit 7 set)
$CF	Left ('O' with bit 7 set)
$D0	Right ('P' with bit 7 set)
$46	Fire ('F')

Used by the routines at $0800, $184E, $189D, $290F, $2D47, $3940, $39C7 and $BE09.