Reading scancodes

Scancodes are device-level key events, not ASCII. For simple keys, the break code is often the make code with the high bit set. Check the scancode set and extended-byte cases before treating that as a universal rule.

Byte pattern	Meaning
0x1e	A key make code
0x9e	A key break code
0xE0 ...	extended sequence
0x81	ESC break code in these tests

Make means key press. Break means key release. Some keys arrive as multi-byte sequences, and the parser must not report a scancode until the sequence is complete.

Parser state

A correct parser needs state: idle with no prefix, waiting after 0xE0, or holding a complete scancode for the caller. That state belongs in the keyboard library, not in every application loop.

This is the first place where one byte is not always one message. The same idea returns in mouse packets, UART protocols, and file formats: the parser must know when it has enough bytes to describe one event.

Application state

Higher-level code can build "key is currently down" tables, text input, menu actions, or game movement. The low-level parser reports what happened at the device boundary without deciding what the application should do.