Kempston Joystick Interface

I haven't checked it out yet, but in a previous posting you were looking 
for help with joysticks. The only joystick I know about is the Kempston
joystick. It operated on port 0x1f and corresponding ports. Using the
following masks

	FIRE 	0x10
	UP   	0x08
	DOWN 	0x04 
	LEFT	0x02
	RIGHT 	0x01

tells you what position the joystick is in.

how do I read the Kempston Joystick? 
 
	IN 31
 
The answer is usually 0 (or 255 if it isn't plugged in at all), 
with bits set for directions pressed.