I did lower the baud rate , the baud now is only 2400.
I 've tried to test the communication again with a very simple code but that problem still happens:
Here is the MCU code:
ORG 0
MAIN:
MOV SCON,#42H
MOV TMOD,#25H
MOV TH1,#-12 ;BAUD=2400BAUD
SETB TR1
SETB TR0
MOV R2,#66
MOV R3,#77
MOV R5,#88
MOV R6,#99
DATA_OUT:
JNB TI,$
CLR TI
CLR TR1
SETB TR1
MOV SBUF,R2
JNB TI,$
CLR TI
CLR TR1
SETB TR1
MOV SBUF,R3
JNB TI,$
CLR TI
CLR TR1
SETB TR1
MOV SBUF,R5
JNB TI,$
CLR TI
CLR TR1
SETB TR1
MOV SBUF,R6
JMP DATA_OUT
END
-----------------------------------
Visual reads firstly very correctly 66 77 88 99
and then sometimes 77 88 99 66
---------------------------------
I use Max232 and no opto to couple the board with PC.
After receive the data from buffer I did clear the buffer by setting Mscomm.inbuffercount=0
In the worst case, I will redesign the board to use handshaking but would you please give me some info about that technique.
Thanks a lot for all of your help