From Retrosoftware

Current revision

Read the Joystick

Uses OSBYTE &80:

In:

X = 0 Read Fire Buttons Return value in X

X = 1 Read X Axis Return value in Y;X ( Returns 0 - 65535 Right Low, Left High )

X = 2 Read Y Axis Return value in Y;X ( Returns 0 - 65535 Down Low, Up High )

The Code

JOY_RIGHT        = 1
JOY_LEFT           = 2
JOY_DOWN        = 4
JOY_UP		= 8
JOY_FIRE	        = &10

JoyBits 	        = &70


._READ_JOYSTICK:
	LDA 	#&00
	STA 	JoyBits

.left_right:
	LDX	#1
	LDA 	#&80
	JSR 	_OSBYTE
	LDA	#0
	CPY 	#&25
	BCS 	not_right
	ORA 	#JOY_RIGHT
.not_right:
	CPY 	#&DB
	BCC 	not_left
	ORA 	#JOY_LEFT
.not_left:
	STA 	JoyBits

.up_down:
	LDX 	#&02
	LDA 	#&80
	JSR 	_OSBYTE
	LDA 	JoyBits
        CPY 	#&25
	BCS 	not_down
  	ORA 	#JOY_DOWN
.not_down:
	CPY 	#&DB
	BCC 	not_up
	ORA 	#JOY_UP
.not_up:
   	STA 	JoyBits

        LDX 	#&00
	LDA 	#&80
	JSR 	_OSBYTE
	TXA
	LSR 	A
	BCC 	not_fire

	LDA 	JoyBits
	ORA 	#JOY_FIRE
	STA 	JoyBits

.not_fire:
	RTS