KERNAL_CLEAR_SCREEN = $e544 ; KERNAL ROM routine.
VICSCN              = $0400 ; VIC-II Screen Video Matrix, 1024 (int).
* = $8000
 
     .word coldstart            ; coldstart vector
     .word warmstart            ; warmstart vector
     .byte $C3,$C2,$CD,$38,$30  ; "CBM8O". Autostart string
 
coldstart
     sei
     stx $d016
     jsr $fda3 ;Prepare IRQ
     jsr $fd50 ;Init memory. Rewrite this routine to speed up boot process.
     jsr $fd15 ;Init I/O
     jsr $ff5b ;Init video
     cli
 
warmstart
; Insert your code here
     jsr KERNAL_CLEAR_SCREEN

     ; read string by byte into vram until null byte
     ldx #0
loop
     lda my_string,x
     cmp #$00
     beq bail
     sta VICSCN,x
     inx
     jmp loop
bail
     ; pretty colors
     inc $d020
     jmp *-3

; macro to convert ASCII text here to native screen codes
.enc "screen"
my_string .null "HELLO WORLD!"
.enc "none"
 
* = $9fff                     ; fill up to 8k or cartconv will fail
     .byte 0