Sabre Wulf: Routine at 45273

45273: Controls: Kempston Joystick

Used by the routine at HandlerControls.

Output
C	Joystick controls

ReadKempstonJoystick

45273

IN A,(31)

A=controls.

Initialise the controls as "none" in C.

45275

LD C,0

C=0.

Check joystick "RIGHT".

ReadKempstonJoystick_Right

45277

BIT 0,A

If bit 0 is set/ "RIGHT" is NOT being pressed then jump to ReadKempstonJoystick_Left.

45279

JR Z,ReadKempstonJoystick_Left

If not jump to ReadKempstonJoystick_Left.

45281

SET 1,C

Set bit 1 of C.

Check joystick "LEFT".

ReadKempstonJoystick_Left

45283

BIT 1,A

If bit 1 is set/ "LEFT" is NOT being pressed then jump to ReadKempstonJoystick_Down.

45285

JR Z,ReadKempstonJoystick_Down

If not jump to ReadKempstonJoystick_Down.

45287

SET 0,C

Set bit 0 of C.

Check joystick "DOWN".

ReadKempstonJoystick_Down

45289

BIT 2,A

If bit 2 is set/ "DOWN" is NOT being pressed then jump to ReadKempstonJoystick_Up.

45291

JR Z,ReadKempstonJoystick_Up

If not jump to ReadKempstonJoystick_Up.

45293

SET 3,C

Set bit 3 of C.

Check joystick "UP".

ReadKempstonJoystick_Up

45295

BIT 3,A

If bit 3 is set/ "UP" is NOT being pressed then jump to ReadKempstonJoystick_Fire.

45297

JR Z,ReadKempstonJoystick_Fire

If not jump to ReadKempstonJoystick_Fire.

45299

SET 2,C

Set bit 2 of C.

Check joystick "FIRE".

ReadKempstonJoystick_Fire

45301

AND %00010000

Keep only bit 4.

45303

OR C

Merge the kept bit into C.

45304

LD C,A

45305

RET

Return.