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(From the IBM 3270 terminal's Programmed Function Keys (PF keys)) One of a set of special keys on a computer or terminal keyboard which can be programmed so as to cause an application program to perform certain actions.
Function keys on a terminal may either generate short fixed sequences of characters, often beginning with the escape character (ASCII 27), or the characters they generate may be configured by sending special character sequences to the terminal.
On a microcomputer keyboard, the function keys may generate a fixed, single byte code, outside the normal ASCII range, which is translated into some other configurable sequence by the keyboard device driver or interpreted directly by the application program.