hi.. for all,
I will give more information about my problem.
I try to connect my pc to mcs51 using SN75176 (RS485). It must to do communication (transmit and receive). I use PC with CPU 486, and rate transfer 1200 bps via com1.
I use QBASIC program to operate the communication.
For example, I transmit a character to mcs51 and then mcs51 reply to pc.
To erik malund, would you give me a standart (ESSENTIAL) waiting time before mcs51 reply to pc?
Is the standart time can work to the other pc (higher speed)?
I already to made a communication, but can not working to the other PC (different type of CPU).
Please give me program example or information about this topik.

thank you verymuch.

ivan.