frank197662:
Could I write a program for control 8 arduino devices (MEGA 2560 R3 ) on pc via rs 232 , that mean is control 8 com port at the same time?
Have you considered connecting one Mega to your PC and connecting the other Megas to the first one rather than to the PC?
If you tell us all about the project you are trying to create it will be much easier to help.
...R