🖮 CICS

Introduction to CICS

Beginner 🕑 20 min read 👁 5 views

What is CICS?

CICS (Customer Information Control System) is IBM's transaction processing system for mainframes. It enables online, real-time transaction processing for business applications.

CICS Components

Transaction - Unit of work (4-char ID)
Program - Application code
Terminal - User interface device
File - Data storage
Queue - Temporary/transient data

CICS Services

Program Control - LINK, XCTL, RETURN
Terminal Control - SEND, RECEIVE
File Control - READ, WRITE, REWRITE
Queue Control - WRITEQ, READQ
Interval Control - DELAY, POST, WAIT

CICS-COBOL Interface

CICS commands are embedded in COBOL using:

EXEC CICS command options END-EXEC.

CICS Areas

EIB - Execute Interface Block (system info)
COMMAREA - Communication area between programs
TWA - Transaction Work Area
CWA - Common Work Area

Common EIB Fields

Field	Description
EIBCALEN	COMMAREA length
EIBTRNID	Transaction ID
EIBTRMID	Terminal ID
EIBDATE	Date (0CYYDDD)
EIBTIME	Time (0HHMMSS)
EIBRESP	Response code

Code Example

       IDENTIFICATION DIVISION.
       PROGRAM-ID. CICSPROG.

       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 WS-MESSAGE      PIC X(50).
       01 WS-RESPONSE     PIC S9(8) COMP.
       01 WS-LENGTH       PIC S9(4) COMP.

       01 WS-COMMAREA.
          05 CA-FUNCTION  PIC X(1).
          05 CA-EMP-ID    PIC 9(6).
          05 CA-EMP-NAME  PIC X(30).
          05 CA-RETURN-CD PIC 9(2).

       LINKAGE SECTION.
       01 DFHCOMMAREA     PIC X(39).

       PROCEDURE DIVISION.

           IF EIBCALEN = 0
      *        FIRST TIME - NO COMMAREA
               MOVE "WELCOME TO CICS" TO WS-MESSAGE
               PERFORM SEND-MESSAGE
           ELSE
      *        RETURNING WITH DATA
               MOVE DFHCOMMAREA TO WS-COMMAREA
               PERFORM PROCESS-REQUEST
           END-IF.

           EXEC CICS RETURN
               TRANSID('MENU')
               COMMAREA(WS-COMMAREA)
               LENGTH(39)
           END-EXEC.

       SEND-MESSAGE.
           MOVE 50 TO WS-LENGTH.
           EXEC CICS SEND
               FROM(WS-MESSAGE)
               LENGTH(WS-LENGTH)
               ERASE
           END-EXEC.

       PROCESS-REQUEST.
           EVALUATE CA-FUNCTION
               WHEN 'I'
                   PERFORM INQUIRY-LOGIC
               WHEN 'A'
                   PERFORM ADD-LOGIC
               WHEN 'U'
                   PERFORM UPDATE-LOGIC
               WHEN OTHER
                   MOVE '99' TO CA-RETURN-CD
           END-EVALUATE.