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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
set_memory:
ldy #$0
ldx #$FF
set_memory_loop:
sty $0, x
iny
dex
bne set_memory_loop
test_memory:
ldy #$0
ldx #$FF
test_memory_loop:
tya
pha
lda $0, x
cmp $1FF ; stack was empty so Y is now on top of stack
bne test_memory_bad
pla
tay
iny
dex
bne test_memory_loop
jmp test_memory_ok
test_memory_bad:
ldx #0
msg_loop_bad:
lda message_memory_bad, x
beq msg_end_bad
jsr lcd_send_data
inx
jmp msg_loop_bad
msg_end_bad:
jmp finish
test_memory_ok:
ldx #0
msg_loop_ok:
lda message_memory_ok, x
beq msg_end_ok
jsr lcd_send_data
inx
jmp msg_loop_ok
msg_end_ok
finish:
jmp finish
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 #$0 ; clear RS/RW/E
sta PORTA
rts
lcd_send_data:
jsr lcd_wait
sta PORTB ; data to send to port B
lda #RS ; clear RW, E, set RS for data
sta PORTA
lda #( E | RS ) ; clear RW, set E/RS, send data
sta PORTA
lda #RS ; clear RS, E, keep RS
sta PORTA
rts
nmi:
rti
irq:
rti
message_memory_bad:
.asciiz "mem bad"
message_memory_ok:
.asciiz "mem ok"
.org #$fffa
.word nmi
.word reset
.word irq
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