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|
PORTB = $6000
PORTA = $6001
DDRB = $6002
DDRA = $6003
E = %10000000
RW = %01000000
RS = %00100000
.org #$f800
reset:
ldx #$FF ; initialize call stack to $1FF
txs
lda #%11111111 ; set output on all pins of PORTB
sta DDRB
lda #%11100000 ; set output on LCD control pins of PORTA
sta DDRA
lda #%00111000 ; set 8-bit, 2-line display, 5x8 font
jsr lcd_send_command
lda #%00001110 ; display on, cursor on, no blink
jsr lcd_send_command
lda #%00000001 ; clear display
jsr lcd_send_command
lda #%00000010 ; return home
jsr lcd_send_command
lda #%00000110 ; set entry mode: increment, no shift
jsr lcd_send_command
cli ; allow interrupts now, LCD is ready
msg_again:
ldx #0
msg_loop:
lda message, x ; string to send
beq msg_end
jsr lcd_send_data
inx
jmp msg_loop
msg_end:
jmp msg_again
term:
jmp term
lcd_wait:
pha
lda #%00000000 ; port B to all input
sta DDRB
lcd_wait_loop:
lda #RW
sta PORTA
lda #(RW | E)
sta PORTA
lda PORTB
and #%10000000
bne lcd_wait_loop
lda #RW
sta PORTA
lda #%11111111 ; port B back to output
sta DDRB
pla
rts
lcd_send_command:
jsr lcd_wait
sta PORTB
lda #$0 ; clear RS/RW/E
sta PORTA
lda #E ; clear RS/RW, set E, send instruction
sta PORTA
lda #$0 ; clear RS/RW/E
sta PORTA
rts
lcd_send_data:
jsr lcd_wait
sta PORTB ; data to send to port B
lda #RS ; clear RW, E, set RS for data
sta PORTA
lda #( E | RS ) ; clear RW, set E/RS, send data
sta PORTA
lda #RS ; clear RS, E, keep RS
sta PORTA
rts
nmi:
pha
lda #'I'
jsr lcd_send_data
pla
rti
irq:
pha
lda #'i'
jsr lcd_send_data
pla
rti
message:
.asciiz "6502 "
.org #$fffa
.word nmi
.word reset
.word irq
|
