Character Codes - IBM AT 5170 Technical Reference

layout. Some operating systems may make provisions for
alternate keyboard layouts by providing an interrupt replacer,
which resides in the read/write memory. This section discusses
only the ROM routine.
Extended ASCII encompasses I-byte character codes, with
possible values of 0 to 255, an extended code for certain extended
keyboard functions, and functions handled within the keyboard
routine or through interrupts.
Character Codes
The character codes described later are passed through the BIOS
keyboard routine to the system or application program. A
"-1"
means the combination is suppressed in the keyboard routine.
The codes are returned in the AL register. See "Characters,
Keystrokes, and Color" later in this manual for the exact codes.
5-14 System BIOS