Casio IT-2000W manual Keyboard Control, System Scanning Code, Primary/Secondary Code, Primary code

6.2Keyboard Control

The keyboard control of IT-2000 is compatible with the IBM PC/AT. The keyboard controller senses if a key has been pressed and sends a MAKE or BREAK code to the main CPU.

Application Program

Function Process

BIOS

Hardware Interrupt Process

Primary/Secondary Code

Keyboard

Input Buffer

System Scanning Code

Sub-CPU

Keyboard

Fig. 6.2

System Scanning Code

Each keyboard scanning code generated from the keyboard main unit will be converted to the keyboard system scanning code through the controller.

MAKE code	: Code generated when the corresponding key is pressed.
BREAK code	: Code generated when the corresponding key is released.

Primary/Secondary Code

A code generated if an INT09h interrupt occurs will be converted to a primary code and a secondary code through the BIOS and set in the key buffer. They can be acquired from the application program by calling INT16h.

Primary code

Basically a character code (refer to the code table on the next page) is assigned to each key, except that 00h is assigned to function keys (Fn+ 0 to Fn+ 6), which must be recognized together with a secondary code as a set.

88