Reading MD3 Joypad

Details

All the buttons can't be read at once. There is a multiplexer inside the control pad.

Reading the 3 buttons pad consist of 5 steps :

• Set the direction of pin 6 to output and all others to input.
• Set TH (pin6) to 1.
• Read the first part of the buttons (UP,DOWN,LEFT,RIGHT,B,C)
• Switch the outputs in the control pad by setting TH (pin6) to 0.
• Read the second part of the buttons (A,START)

TH State	Data
1	Bit 7 6 5 4 3 2 1 0 Def 0 TH C B RIGHT LEFT DOWN UP
0	Bit 7 6 5 4 3 2 1 0 Def 0 TH START A 0 0 DOWN UP

Code

 	moveq	#0, d0
	moveq	#0, d1

	move.b  #0x40, (0xA10009)	| Set direction
	move.b  #0x40, (0xA10003)	| TH = 1
	nop
	nop
	move.b  (a0), d0		| d0.b = X | 1 | C | B | R | L | D | U |
	andi.b	#0x3F, d0		| d0.b = 0 | 0 | C | B | R | L | D | U |

	move.b	#0x0, (0xA10003)	| TH = 0
	nop
	nop
	move.b	(0xA10003), d1		| d1.b = X | 0 | S | A | 0 | 0 | D | U |
	andi.b	#0x30, d1		| d1.b = 0 | 0 | S | A | 0 | 0 | 0 | 0 |
	lsl.b	#0x2, d1		| d1.b = S | A | 0 | 0 | D | U | 0 | 0 |
	or.b	d1, d0			| d0.b = S | A | C | B | R | L | D | U |