AID (Attention Identifier) keys are special keys on a 3270 terminal keyboard that send a signal to CICS, indicating that the user has completed an action. These keys are used to trigger transaction processing, navigate between screens, or execute commands.

DFHAID is the system-defined copybook for AID keys, having definitions for the ENTER key, PF1 to PF24, PA1 to PA3, and CLEAR keys. AID keys can be included in the application program by copying the library member DFHAID (COPY DFHAID).

Some of the common AID keys and its function -

AID Key	Function
ENTER	Sends data to the CICS application.
PF1 - PF24	Function keys
CLEAR	Clears the screen.
PA1 - PA3	Program attention keys used for system-level interactions.

DFHAID Copybook layout with full set of keys specified below -

COPY DFHAID.

The copybook expansion look like -

*COPY DFHAID
 01 DFHAID.
   02  DFHNULL   PIC  X  VALUE IS ' '.
   02  DFHENTER  PIC  X  VALUE IS ''''.
   02  DFHCLEAR  PIC  X  VALUE IS '_'.
   02  DFHCLRP   PIC  X  VALUE IS '¦'.
   02  DFHPEN    PIC  X  VALUE IS '='.
   02  DFHOPID   PIC  X  VALUE IS 'W'.
   02  DFHMSRE   PIC  X  VALUE IS 'X'.
   02  DFHSTRF   PIC  X  VALUE IS 'h'.
   02  DFHTRIG   PIC  X  VALUE IS '"'.
   02  DFHPA1    PIC  X  VALUE IS '%'.
   02  DFHPA2    PIC  X  VALUE IS '>'.
   02  DFHPA3    PIC  X  VALUE IS ','.
   02  DFHPF1    PIC  X  VALUE IS '1'.
   02  DFHPF2    PIC  X  VALUE IS '2'.
   ... 
   02  DFHPF23   PIC  X  VALUE IS '.'.
   02  DFHPF24   PIC  X  VALUE IS '<'.

How it works?

• A user presses an AID key (e.g., ENTER, PF3, PF7) on a 3270 terminal.
• CICS detects the keypress and stores the corresponding AID value.
• The program retrieves the AID value using the EIBAID field in the CICS EXEC Interface Block (EIB).
• The program processes the request based on the AID key pressed.

Once the AID key is pressed, CICS stores the information in the EIBAID field. We then need to compare the EIBAID value with each field definition from DFHAID to determine which functional key was pressed. The validation process shown below -

EVALUATE TRUE
    WHEN EIBAID = DFHENTER 
         PERFORM PROCESS-ENTER-LOGIC
    WHEN EIBAID = DFHPF3 
         PERFORM PROCESS-EXIT-LOGIC
    WHEN EIBAID = DFHPF7  
         PERFORM PROCESS-SCROLL-UP-LOGIC
END-EVALUATE.

Short Examples -

Scenario - COBOL program reads user input and determines the action based on the AID key pressed.

...
DATA DIVISION.
WORKING-STORAGE SECTION.
...
PROCEDURE DIVISION.

    EXEC CICS RECEIVE
         MAP('SCREEN1')
         MAPSET('MAPSET1')
         INTO(WS-MESSAGE)
         END-EXEC.

    EVALUATE TRUE
        WHEN EIBAID = DFHENTER 
             PERFORM PROCESS-ENTER-LOGIC
        WHEN EIBAID = DFHPF3 
             PERFORM PROCESS-EXIT-LOGIC
        WHEN EIBAID = DFHPF7  
             PERFORM PROCESS-SCROLL-UP-LOGIC
    END-EVALUATE.
	
    ...

The program receives input from the user and checks the AID key using EIBAID. If the ENTER key (DFHENTER) is pressed, the program processes the input. If PF3 (DFHPF3) is pressed, the program exits. If PF7 (DFHPF7) is pressed, the screen scrolls up. For any other AID key, no action is taken.

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