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Function Key

Enhanced Definition

In the mainframe context, a Function Key (often referred to as a Program Function key or PF key, or Program Attention key or PA key) is a special key on a 3270 terminal or emulator keyboard used to trigger predefined actions or commands within a mainframe application or system component, such as ISPF, TSO/E, or CICS. These keys provide a quick, single-key method for users to interact with screen-based applications without typing full commands.

Key Characteristics

- Types of Keys: Primarily PF (Program Function) keys, typically PF1 through PF24, and PA (Program Attention) keys, PA1, PA2, PA3. Other special keys like Clear, Enter, and SysReq also serve similar roles.
- Application-Specific Mapping: The action performed by a function key is almost always context-sensitive and determined by the specific mainframe application or panel currently displayed.
- 3270 Terminal Interaction: Function keys are fundamental to the user interface of 3270 terminals and their emulators, which operate in a block-mode fashion where input is sent to the host only after a special key (like Enter or a PF key) is pressed.
- Hardware vs. Emulator: On physical 3270 terminals, these keys are dedicated hardware buttons. In modern environments, 3270 emulators map these keys to standard PC keyboard keys (e.g., F1 on a PC keyboard often maps to PF1 on a 3270 emulator).
- Command Abbreviation: They serve as an abbreviation for longer commands or sequences of actions, significantly enhancing user productivity and navigation.

Use Cases

- ISPF Navigation: Pressing PF3 to exit a panel, PF7 to scroll up, PF8 to scroll down, PF10 to scroll left, and PF11 to scroll right in ISPF editors or browse sessions.
- TSO/E Command Execution: Assigning frequently used TSO commands to PF keys for quick execution, such as PF1 for HELP or PF12 for RETRIEVE previous commands.
- CICS Transaction Control: In CICS applications, PF keys are often used to confirm actions, navigate between screens, or trigger specific business logic (e.g., PF12 to cancel a transaction, PF3 to return to a main menu).
- System Monitoring (SDSF): Using PF keys to refresh displays, scroll through job output, or issue line commands in utilities like SDSF (System Display and Search Facility).

Related Concepts

Function keys are intrinsically linked to the 3270 terminal architecture and block -mode communication, where they signal the host to process the screen's contents. They are a cornerstone of the ISPF (Interactive System Productivity Facility) user interface, providing the primary means of navigation and command execution within its hierarchical panel structure. Similarly, TSO/E (Time Sharing Option/Extensions) and applications like CICS (Customer Information Control System) heavily rely on function keys for user interaction, making them a critical component of the overall mainframe user experience and application