Example of writing text to screen using VERA on Commander X16

verahello.asm

!cpu 65c02

; BASIC program ("10 SYS $0810")
*=$0801
	!word	$080C			; Pointer to next BASIC line
	!word	$000A			; Line number $000A = 10
	!byte	$9E			; SYS BASIC token
	!pet	" $810",0		; Address where ASM starts
	!word	$0000			; EOF BASIC program
*=$0810

; VERA registers needed to write characters on the screen.
; https://github.com/commanderx16/x16-docs/blob/master/VERA%20Programmer's%20Reference.md#registers
; It is assumed that the screen is in "normal" 80x60 text mode.
VERA_ADDR_L	= $9F20
VERA_ADDR_M	= $9F21
VERA_ADDR_H	= $9F22
VERA_DATA0	= $9F23

main:
	lda	#%00100000		; Increment 2, High-addr=0
	sta	VERA_ADDR_H
	lda	#30			; Y coordinate (middle of screen)
	sta	VERA_ADDR_M
	lda	#33*2			; X coordinate: (screenwidth/2)-(stringlength/2)
	sta	VERA_ADDR_L		; Multiplied by 2 because in normal screenmode,
					; 1 byte is used for character and 1 for color

	ldy	#0			; Use .Y as index into string
.loop:	lda	my_str,y		; Load character
	beq	.end:			; If it is 0, jump to end
	sta	VERA_DATA0		; Write character to VERA memory, VERA
					; will automaticly add 2 to address.
	iny				; Increment .Y
	bra	.loop:			; Jump back to get next character
.end:
	rts

; Zero terminated "string" encoded to use the default VERA font layout
; See: https://cx16.dk/veratext/
;              H   E   L   L   O   ,       W   O   R   L   D   !
my_str:	!byte $08,$05,$0C,$0C,$0F,$2C,$20,$17,$0F,$12,$0C,$04,$21,$00