The keyboard and the host communicate together using a pre-defined command set, also part of the PS2 protocol. Those commands are detailed analyzed below.

These are the commands that the host will send to the keyboard:

This command is followed by a byte indicating the desired LEDs setting.

When OK, both bytes are acknowledged. If the second byte is recognized as a command, that command is acknowledged and done instead, otherwise a NACK is returned.

This command requests an echo return by the keyboard (again 0xEE).

This command reads a 2-byte keyboard ID. XT keyboards do not answer to this command. AT keyboards will reply with an ACK (0xFA) only. The MF2 and other keyboards will reply with a 2 byte ID. A 10msec delay should be considered after this command.

Following this command is a byte with the desired delay and repeat rate.

where A=Bits 4-3 and B=bits 2-0. By default after reset the delay is 10.9 cps

The keyboard is automatically disabled after every transmission failure. This command re-enables the keyboard and clears its internal 16-byte buffer.

This command resets the keyboard, clears the output buffer, switch off the LEDs, resets repeat rate and delay to defaults and disable the keyboard scan.

This command resets the keyboard, clears the output buffer, switch off the LEDs and resets repeat rate and delay to defaults.

Forces the keyboard to resend the last byte sent.

Reset and runs a self-test. The self-test (BAT) will return aa if OK or fc if there is a problem. During this test, all the LEDs flashes once.

The keyboard will respond to host commands or to external events (like key presses) with it's own commands as follows:

Sends the ACK command to the host when needed.

When the host sends a reset command to the keyboard (ff), it must run a self test and answer with this command.

This command requests an echo return by the host (again 0xEE).

Forces the host to resend the last byte sent.

This command is sent when an error or a buffer overflow occurs.

This command is sent when an error or a buffer overflow occurs.

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