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91 lines
1.4 KiB

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 send_inst
lda #%00001110 ; Display on; cursor on; blink off
jsr send_inst
lda #%00000001 ; Reset display
jsr send_inst
lda #%00000110 ; Increment and shift cursor; don't shift display
jsr send_inst
ldx #0
print:
lda message,x
beq loop
jsr send_data
inx
jmp print
loop:
jmp loop
message: .asciiz "Hello again, Kiddies!"
lcd_wait:
pha
lda #%00000000 ; PORT B to INPUT
sta DDRB
lcd_busy:
lda #RW
sta PORTA
lda #(RW | E)
sta PORTA
lda PORTB
and #%10000000
bne lcd_busy
lda #RW
sta PORTA
lda #%11111111 ; PORT B to output
sta DDRB
pla
rts
send_inst:
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
send_data:
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
.org $fffc
.word reset
.word $0000