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PS/2 Keyboard Commands

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The keyboard processor has two commands that are sent to the host system when a key is pressed: the make and the break command. Each key has a separate code that is sent in each case. The code that is actually sent to the host has no relationship to the ASCII code of the character sent. It is up to the host code to decode the key command sent. For example, the character 5 has the make code 0x2E and the break code 0xF0,0x2E. Most standard characters have a one-byte make code and a two-byte break code, and extended characters often have two-byte make codes and three-byte break codes. 

If a key is pressed, then the make code is sent periodically until another key is pressed. The rate of this is called the typematic rate and is defined as default at approximately 10 characters per second.

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