iTS 1.0+)

Introduction to SCREEN COBOL

Compaq NonStop™ Pathway/iTS SCREEN COBOL Reference Manual—426750-001

1-4

Pathway System Components

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 executes SCREEN COBOL programs. The terminal control

provided by the TCP simplifies your programming task. The TCP is a multithreaded

process that can execute several different SCREEN COBOL programs simultaneously.

The TCP performs the following operations for each SCREEN COBOL program

executed:

•

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.