scancodes

Scancodes are the numeric codes produced by a computer keyboard to report key presses and releases to the host computer. When a key is pressed, the keyboard transmits a make code; when the key is released, it transmits a break code. These codes are the lowest-level representation of keyboard input and are largely independent of character encoding.

In PS/2 and early PC keyboard architectures, several scancode sets exist, notably Set 1, Set 2, and Set 3. Set 1 is common on IBM PC-compatible systems. Some keys are sent with an extended prefix, typically 0xE0, to indicate features like the right-hand Control key or Arrow keys; Pause/Break uses a special sequence and is not a simple pair of make/break codes.

Programming interfaces or firmware translate scancodes into higher-level events, such as ASCII characters or OS-specific key events. The exact mapping from scancodes to characters depends on the keyboard layout and the operating system. In practice, a keyboard driver may expose a unified map from scancodes to virtual key codes, and then to characters, taking layout into account.

With USB keyboards, devices now use the HID (Human Interface Device) protocol and report usage IDs rather than hardware scancodes; computer systems typically translate HID usages into scancodes or key events via a driver. As a result, the term “scancode” is sometimes used to refer to the host-facing code in OS-specific input stacks rather than the physical hardware signal.