Chase H.Q.: Routine at A0CC

A0CC: Keyscan


kempston_flag	A0CC	DEFB $00	Set to 1 if Kempston joystick is chosen, 0 otherwise
keydefs	A0CD	DEFB $25,$22,$20,$23,$1B,$13,$03,$0B	Gear, Accelerate, Brake, Left, Right, Quit, Pause, Turbo
user_input	A0D5	DEFB $00	User input: QPBFUDLR - Quit Pause Boost Fire/Gear Up Down Left Right. Note that attract mode is driven through this var.
This entry point is used by the routines at load_stage, attract_mode, main_loop, run_pregame_screen, check_user_input and page_in_stage_128k.
keyscan	A0D6	LD A,($A0CC)	If not Kempston then goto ks_keyboard
	A0D9	AND A
	A0DA	JR Z,ks_keyboard
	A0DC	IN A,($1F)	Read Kempston joystick port. Returns 000FUDLR active high
	A0DE	AND $1F	Read Kempston joystick port. Returns 000FUDLR active high
	A0E0	PUSH AF
	A0E1	LD E,$20
	A0E3	LD HL,$A0CD
	A0E6	CALL kempston_flag_2
	A0E9	RRCA
	A0EA	RRCA
	A0EB	RRCA
	A0EC	AND $E0
	A0EE	POP DE
	A0EF	OR D
	A0F0	LD E,A
	A0F1	JR ks_common
ks_keyboard	A0F3	LD E,$01
	A0F5	LD HL,$A0CD
	A0F8	CALL kempston_flag_2
ks_common	A0FB	AND $03
	A0FD	CP $03
	A0FF	LD A,E
	A100	JR NZ,kempston_flag_0
	A102	AND $FC
	A104	LD E,A
kempston_flag_0	A105	AND $0C
	A107	CP $0C
	A109	LD A,E
	A10A	JR NZ,kempston_flag_1
	A10C	AND $F3
kempston_flag_1	A10E	LD ($A0D5),A
	A111	RET	Return
kempston_flag_2	A112	LD A,(HL)	Outer keyboard loop
	A113	INC HL
	A114	CALL keyscan_inner
	A117	CCF	invert carry
	A118	RL E
	A11A	JR NC,kempston_flag_2	loop while top bit set?
	A11C	LD A,E
	A11D	RET	Return
keyscan_inner	A11E	LD C,A	Inner keyboard loop.... what's in A?
	A11F	AND $07	B=(A&7)+1, C=5-(A>>3)
	A121	INC A
	A122	LD B,A
	A123	SRL C
	A125	SRL C
	A127	SRL C
	A129	LD A,$05
	A12B	SUB C
	A12C	LD C,A
	A12D	LD A,$FE	A = $FE ROR B
kempston_flag_3	A12F	RRCA
	A130	DJNZ kempston_flag_3
	A132	IN A,($FE)	Port $FE is the AND of all columns/rows? This is the main keyboard access
kempston_flag_4	A134	RRA	C = A ROR C
	A135	DEC C
	A136	JR NZ,kempston_flag_4
	A138	RET	Return