Problem- CNC Programming

[sabreen]

Hi every one, I have a FMS contains a cnc lathe ,cnc mill,and robot moves on conveyor, and main computer to control the system, to execute a certain machaining program on one of the two machaines I go to the edit mode on the main computer and select the program then I go to the execute mode to execute that program.
the problem is that I want to select and execute the machining program automaticaly without logging to the graphical user interface modes(edit and execute modes), depending on a signal comming from the port ,when I recieve a value of one on the serial port, the system automaticaly select and execute the program number 1, and when I recieve a value of 2 , the program number 2 is selected and executed.

the software environment is ATFLEX, under dos, win95.

pls help