Hi to all. Someone could to find my trouble?
The point is I am doing a minimum system with a 80C52 from ATMEL. I need write & read characters by serial port, I was looking here in 8052.com many information about, this site is wonderful to help us.
OK the small program I did send characters to the buffer, and this could sent to a computer using SP232A (MAX232) interfase. I tested the SP232A and is working ok, I tested PO & P2 from microcontroller and is working ok too, I can see the wave form by a LOGIC DART of HP, but I can not see any wave form at P3.1 (TXD), and I don`t know why. THIS PROGRAM RUNS OK AT SIMULATOR.
The small program to test serial port is:
ORG
LJMP MAIN
ORG 0023H
LJMP SPISR
ORG 0030H
MAIN: MOV TMOD,#20H ; TIMER 1 MODE2
MOV TH1,#-3 ; 9600 BAUD RATE
SET TR1
MOV SCON,#42H
MOV A,#054H
MOV IE,#90H
SPISR: CJNE A,#7FH, SKIP
MOV A,#20H
SKIP : MOV SBUF,A
INC A RETI