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

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

  .org $8000

reset:
  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 command_to_lcd
  lda #%00001110	; set display and curson on, do not blink
  jsr command_to_lcd
  lda #%00000110	; set entry mode increment and display shift off
  jsr command_to_lcd
  lda #%00000001
  jsr command_to_lcd

  ldx #0
print:
  lda message,x
  beq loop ; load sets zero flag (checked by beq) when it loads a zero byte.
  jsr ASCII_to_lcd
  inx
  jmp print

loop:
  jmp loop

; asciiz appends a 0 byte to the string
message: .asciiz "Hello, world! :D"

lcd_wait:
  pha				; save porta to stack
  lda #%00000000	; set PORTB to input
  sta DDRB
lcdbusy:
  lda #RW
  sta PORTA
  lda #(RW | E)
  sta PORTA
  lda PORTB
  and #%10000000	; check LCD busy flag
  bne lcdbusy		; branch if it is NOT set
  
  lda #RW
  sta PORTA
  lda #%11111111	; set PORTB to output again
  sta DDRB
  pla				; load stack value back to porta
  rts ; RETURN
  
command_to_lcd:
  jsr lcd_wait		; ensure LCD is not busy before sending instruction
  sta PORTB
  lda #0 			; clear RS/RW/E bits
  sta PORTA
  lda #E			; set enable bit to send instruction
  sta PORTA
  lda #0 			; clear RS/RW/E bits
  sta PORTA
  rts ; RETURN

ASCII_to_lcd:
  jsr lcd_wait		; ensure LCD is not busy before sending instruction
  sta PORTB
  lda #RS			; RS set
  sta PORTA
  lda #(RS | E)		; RS and E set
  sta PORTA
  lda #RS			; RS set
  sta PORTA
  rts ; RETURN

  .org $fffc
  .word reset
  .word $0000