Casio IT-2000W - Manual (Page 88)

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6.2 Keyboard 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.
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.
Application Program
Sub-CPU
Function Process
Hardware Interrupt Process
BIOS
Keyboard
System Scanning Code
Primary/Secondary Code
Keyboard
Input Buffer