The corresponding break code for a key is composed of the prefix byte F0h, followed by the make code for that key. The extended keys are recognizable by the E0h prefix to their make codes. Most scan codes are a single byte in length, with the exception of some of the extended keys (e.g. This additional transmitted code is called a 'break' code.
When a pressed key is released, an additional scan code is sent to the host to let it know that the key that was pressed has now been released. It should be noted that if more than one key is pressed and held down, typematic mode only applies to the last key pressed. If a key is held down without being released, the make code for that key will be sent continuously, in accordance with the defined auto-repeat (typematic) rate. The transmitted code is called a scan code and is further sub-classed as a 'make' code in the case of a key being pressed.
With the aid of ASCII look-up tables, the host can determine the function of the pressed key. When a key on the keyboard is pressed, a code is sent to the host CPU.
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