Casio IT-2000D - Manual (Page 154)

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Keypad Driver
As internal process, this library calls the keypad driver (KEYPAD.EXE). The relation among this
library, the keypad driver and BIOS is as follow.
Fig. 7.13
Transition of Keypad State
The following shows the transition of keypad when it is operated.
Input pad for lower-case characters Input pad for upper-case characters
Input pad for controls
Fig. 7.14
Application
Dedicated Library Standard C-language Library
INT85H
Process of Touch Panel INT16HOOK
MS-DOS
INT21H
INT16 BIOS
Press Shift
Press Ctrl Press Ctrl
Key Input Key Input