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CICS Display System

IBM 3270 Terminal:

The 3270 Information Display System is a family of display and printer terminals. 3270 terminals were being used to connect to the mainframe via IBM controllers. Today, 3270 emulation software is available which means that even normal PCs can be used as 3270 terminals. 3270 terminals are dumb terminals and do not do any processing themselves. All processing needs to be done by the application program.

IBM terminals consist of the following components:

CRT Monitor:

The CRT monitor displays the output or the input fields of the application program. A screenshot of a 3278 Model of CRT monitor is shown below. It has the following characteristics:

  1. It is capable of displaying 1920 characters.

  2. Each of these 1920 character positions is individually addressable.

  3. A COBOL application program can send data to all the positions on the screen.

  4. The display characteristics like intensity, protected, non-protected of the field can be set using BMS which we will be discussing in detail in upcoming modules.



IBM keyboard keys are divided into following two categories:

  1. Non-AID Keys – All other keys for alphabets, numeric, punctuation and special characters. are Non-Aid keys. When the user types text or numbers using non-aid keys, CICS will not even know if the user is typing anything or not.

  2. AID Keys – AID keys are known as Attention Identifier Keys. CICS can detect only AID keys. After typing all the input, only when the user presses one of the AID keys, CICS takes control. AID Keys : ENTER, PF1 to PF24, PA1 to PA3, CLEAR.

    AID keys are further divided into two categories:
    • PF Keys – PF keys are known as function keys. PF keys allow transfer of data from terminal to CICS. PF Keys are ENTER and PF1 to PF24.

    • PA Keys – PA keys are known as Program Access keys. PA keys do not allow transfer of data between terminal and CICS. PA Keys are PA1 to PA3 and CLEAR.

If you have any doubts or queries related to this chapter, get them clarified from our Mainframe experts on ibmmainframer Community!

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