Hello-World-Delay.s

PORTB = $6000
PORTA = $6001
DDRB = $6002
DDRA = $6003

E  = %10000000
RW = %01000000
RS = %00100000

  .org $8000

reset:
  ldx #$ff
  txs

  lda #%11111111 ; Set all pins on port B to output
  sta DDRB
  lda #%11100000 ; Set top 3 pins on port A to output
  sta DDRA

  lda #%00111000 ; Set 8-bit mode; 2-line display; 5x8 font
  jsr lcd_instruction
  lda 50
  jsr _delay_ms 
  lda #%00001110 ; Display on; cursor on; blink off
  jsr lcd_instruction
  lda 50
  jsr _delay_ms 
  lda #%00000110 ; Increment and shift cursor; don't shift display
  jsr lcd_instruction
  lda 50
  jsr _delay_ms 
  lda #$00000001 ; Clear display
  jsr lcd_instruction
  lda 50
  jsr _delay_ms 

  ldx #0
print:
  lda message,x
  beq loop
  jsr print_char
  inx
  jmp print

loop:
  jmp loop

message: .asciiz "Hello, world!"

lcd_wait:
  pha
  lda #%00000000  ; Port B is input
  sta DDRB
lcdbusy:
  lda #RW
  sta PORTA
  lda #(RW | E)
  sta PORTA
  lda PORTB
  and #%10000000
  bne lcdbusy

  lda #RW
  sta PORTA
  lda #%11111111  ; Port B is output
  sta DDRB
  pla
  rts

lcd_instruction:
  jsr lcd_wait
  sta PORTB
  lda #0         ; Clear RS/RW/E bits
  sta PORTA
  lda #E         ; Set E bit to send instruction
  sta PORTA
  lda #0         ; Clear RS/RW/E bits
  sta PORTA
  rts

print_char:
  jsr lcd_wait
  sta PORTB
  lda #RS         ; Set RS; Clear RW/E bits
  sta PORTA
  lda #(RS | E)   ; Set E bit to send instruction
  sta PORTA
  lda #RS         ; Clear E bits
  sta PORTA
  rts
_delay_ms:          
  sta tmp1      ; 3
  txa           ; 2
  pha           ; 3
  tya           ; 2
  pha           ; 3
  ldx tmp1      ; 3
  ldy #190      ; 2
@loop1:             
  dey           ; 190 * 2
  bne @loop1    ; 190 * 3 - 1

@loop2:             
  dex           ; 2
  beq @return   ; (x - 1) * 2 + 3

  nop           ; 2
  ldy #198      ; 2
@loop3:             
  dey           ; 198 * 2
  bne @loop3    ; 198 * 3 - 1

  jmp @loop2    ; 3

@return:            
  pla           ; 4
  tay           ; 2
  pla           ; 4
  tax           ; 2
  lda tmp1      ; 3
  rts           ; 6 (+ 6 for JSR)

  .org $fffc
  .word reset
  .word $0000