Thanks for the help, but nothing worked. Here is the code I use:

.include <reg535.def>
.segment start, org $0

en = P1.7
rw = P1.5
rs = P1.3
data = P4

mov dptr,#0ffffh
acall timeout
mov a,#38h
acall sendcommand
mov a,#38h
acall sendcommand
mov a,#0eh
acall sendcommand
mov a,#06h
acall sendcommand
mov a,#01h
acall sendcommand
mov A,#'X'
acall sendtext
clr P3.5
wait:
ajmp wait

sendcommand:
clr rs
clr rw
clr en
mov data,a
setb en
mov dptr,#01ffh
acall timeout
clr en
ret

sendtext:
setb rs
clr rw
clr en
mov data,a
setb en
mov dptr,#01ffh
acall timeout
clr en
ret

timeout:
push 0
push 1
mov R0,DPH
wait2: mov R1,DPL
wait1:
nop
nop
djnz R1,wait1
djnz R0,wait2
pop 1
pop 0
ret


The LCD is connected to this development board. Is it really too difficult or am I just too stupid?