Hi Carlos,

to affect only a single port pin there are powerful bit instructions available on the 8051.
To read constant data from the program memory the "MOVC" was made.
Following an example for your task:


Peter

<pre>
clk_in equ p3.4
data_out equ p1.0

main:
mov dptr, #message
call send_message
jmp main

message:
db message_end - message_start
message_start:
db 1, 2, 3, 10, 20 ;some bytes to send
message_end:

send_message:
clr a
movc a, @a+dptr
mov r7, a ;get number of bytes
send_byte_loop:
inc dptr
clr a
movc a, @a+dptr
mov r6, #8
send_bit_loop:
rlc a ;rotate bits over CY
jnb clk_in, $
jb clk_in, $ ;1-0 transition detect
mov data_out, c ;write bit from CY to pin
djnz r6, send_bit_loop
djnz r7, send_byte_loop
ret