Character Codes - IBM 5170 Technical Reference

Extended ASCII encompasses one-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 following character codes are passed through the BIOS
keyboard routine to the system or application program. A-I
means the combination is suppressed in the keyboard routine.
The codes are returned in the AL register. See Section 7 for the
exact codes.
System BIOS 5-13