Keys marked as “not typematic” generate one stream of bytes without corresponding break scan code bytes (actually the break codes are part of the make code).

The PS/2 models have three make/break scan code sets. The first set matches the PC & XT make/break scan code set and is the one listed here. Scan code sets are selected by writing the value F0 to the keyboard via the 8042 (port 60h). The following is a brief description of the scan code sets (see the PS/2 Technical Reference manuals for more information on scan code sets 2 and 3):

• set 1, each key has a base scan code. Some keys generate extra scan codes to generate artificial shift states. This is similar to the standard scan code set used on the PC and XT.
• set 2, each key sends one make scan code and two break scan codes bytes (F0 followed by the make code). This scan code set is available on the IBM AT also.
• set 3, each key sends one make scan code and two break scan codes bytes (F0 followed by the make code) and no keys are altered by Shift/Alt/Ctrl keys.
• typematic scan codes are the same as the make scan code

Some Tandy 1000's do not handle Alt key combinations when multiple shift keys are pressed. The Alt-Shift-H combination loses the Alt.

extended keys like (F11, F12) can only be read with systems that have extended keyboard BIOS support (or INT 9 extensions); to read these special keys on these systems INT 16,10 must be used