Pathway/iTS SCREEN COBOL Reference Manual (H06.10+, J06.03+)

Introduction to SCREEN COBOL
HP NonStop Pathway/iTS SCREEN COBOL Reference Manual—426750-003
1-4
Pathway System Components
Section. The Screen Section defines the data fields and other characteristics of a
terminal screen; the Message Section defines the messages sent to, and replies
received from, an intelligent device (or the process that controls it). SCREEN COBOL
verbs allow you to display and accept terminal screen data and to communicate with
intelligent devices.
SCREEN COBOL source code is not compiled into machine-language instructions.
The source code is compiled into object code called pseudocode. The pseudocode for
SCREEN COBOL programs is stored in a library and interpreted by the terminal control
process.
Terminal Control Process (TCP)
The TCP interprets and runs SCREEN COBOL programs. The terminal control
provided by the TCP simplifies your programming task. The TCP is a multithreaded
process that can run several different SCREEN COBOL programs simultaneously.
The TCP performs the following operations for each SCREEN COBOL program that is
run:
•
Controls simultaneous execution of the SCREEN COBOL program at several
terminals
•
Maintains separate data areas and control information for each terminal under its
control
•
Performs the physical I/O operations to transmit data to and from terminals
•
Provides a device-independent method of communicating with intelligent devices
•
Performs field validation based on edit symbols in the SCREEN COBOL program
•
Converts data between external and internal representations
•
Sends messages to server processes
•
Returns messages from server processes to appropriate terminals
Instructions to the TCP for checking and converting data are in an object file supplied
as part of the Pathway/iTS product. You can replace these system routines with your
own routines called user-conversion routines.
Figure 1-2 illustrates the TCP executing SCREEN COBOL code on behalf of multiple
terminals. The TCP handles multiple terminals with a single copy of a SCREEN
COBOL program and performs all I/O for the screen displays.