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====== Both joysticks handling plus proper keyboard scan ======

<code>

;64tass format, taken from game SWIV.
;with default $dc02 - $dc03 values ($ff and $00)
;usage : inside irq, jsr j2read (plus jsr j1read if both joysticks will be read).
;and inside irq again (after enough rastertime passes), jsr keyb to read keyboard, standard
;example below.
;all 3 operations are independent and nothing interferes.

;keyb	lda #$f7		;standard keyboard read example
;	sta $dc00
;	lda $dc01
;	and #$20		;scan for key "h"
;	bne +
;	...			;here "h" is pressed
;+	...			;scan for another key

j2v	.byte $00		;backup value
j2f	.byte $00		;fire, $00 no - $10 yes
j2u	.byte $00		;up, $00 no - $01 yes
j2d	.byte $00		;down, $00 no - $01 yes
j2l	.byte $00		;left, $00 no - $01 yes
j2r	.byte $00		;right, $00 no - $01 yes

j2read	lda #$ff
	sta $dc00		;for proper keyboard scan, with joystick scan
	lda $dc00
	eor #$ff
	sta j2v			;inverted value and backupped
	and #$0f
	beq +
	lda #$00		;clear directions
	sta j2u
	sta j2d
	sta j2l
	sta j2r
	lda j2v			;calculate direction
	lsr
	rol j2u
	lsr
	rol j2d
	lsr
	rol j2l
	lsr
	rol j2r
+	lda j2v
	and #$10
	sta j2f			;$10 for fire pressed
	rts

j1v	.byte $00		;backup value
j1f	.byte $00		;fire, $00 no - $10 yes
j1u	.byte $00		;up, $00 no - $01 yes
j1d	.byte $00		;down, $00 no - $01 yes
j1l	.byte $00		;left, $00 no - $01 yes
j1r	.byte $00		;right, $00 no - $01 yes

j1read	lda #$ff
	sta $dc01		;for proper keyboard scan, with joystick scan
	lda $dc01
	eor #$ff
	sta j1v			;inverted value and backupped
	and #$0f
	beq +
	lda #$00		;clear directions
	sta j1u
	sta j1d
	sta j1l
	sta j1r
	lda j1v			;calculate direction
	lsr
	rol j1u
	lsr
	rol j1d
	lsr
	rol j1l
	lsr
	rol j1r
+	lda j1v
	and #$10
	sta j1f			;$10 for fire pressed
	rts

</code>