Help!! How to communicate between From4.5 and Pro*C..

 Hi, experts:

     I am a new user to ORACLE. Use Form4.5 to develop application.  Now I want to communicate the automatic machine by sending some  control code it recognizes by Pro*C. (The diagram show below.)  For example, when operator press a button on Form4.5, the Pro*C should  know what action it take and send the control code to the  Automatic Machine. After Automatic Machine finished its work, it return  value to Pro*C, and the Pro*C pass the return value to Form4.5!!  Does anyone has idea about it? What is the way that PL/SQL communicate  Pro*C? Where to find the description on ORACLE manual?

• -------------------
  | Form 4.5 | | | |-----------|
  | Application|<------->| Oracle <-->Pro*C|<-------> | Automatic |
  |------------| | | RS232 | Machine | Client ------------------- port ------------| (Operator) Server

                 Thanks in advance for help!!!
                                   wangbs from DIMERCO
                                   e-mail: wangbs_at_rs520.ddsc.com.tw