Keyboard Commands & Responses


Commands System Issues to Keyboard (via 8042 port 60h)


	ED  Set/Reset Mode Indicators, keyboard responds with ACK then
	    waits for a following option byte.	When the option byte is
	    received the keyboard again ACK's and then sets the LED's
	    accordingly.  Scanning is resumed if scanning was enabled.
	    If another command is received instead of the option byte
	    (high bit set on) this command is terminated.  Hardware
	    defaults to these indicators turned off.

	    |7-3|2|1|0| Keyboard Status Indicator Option Byte
	      |  | | `--- Scroll-Lock indicator  (0=off, 1=on)
	      |  | `---- Num-Lock indicator  (0=off, 1=on)
	      |  `----- Caps-Lock indicator  (0=off, 1=on)
	      `------- reserved (must be zero)

	EE  Diagnostic Echo, keyboard echoes the EE byte back to the system
	    without an acknowledgement.
	F0  PS/2 Select/Read Alternate Scan Code Sets, instructs keyboard
	    to use one of the three make/break scan code sets.	 Keyboard
	    responds by clearing the output buffer/typematic key and then
	    transmits an ACK.  The system must follow up by sending an
	    option byte which will again be ACK'ed by the keyboard:

	      00  return byte indicating scan code set in use
	      01  select scan code set 1  (used on PC & XT)
	      02  select scan code set 2
	      03  select scan code set 3

	F2  PS/2 Read Keyboard ID, keyboard responds with an ACK and a two
	    byte keyboard ID of 83AB.
	F3  Set Typematic Rate/Delay, keyboard responds with ACK and waits
	    for rate/delay byte.   Upon receipt of the rate/delay byte the
	    keyboard responds with an ACK, then sets the new typematic
	    values and scanning continues if scanning was enabled.
	    
	    |7|6|5|4|3|2|1|0|  Typematic Rate/Delay Option Byte
	     | | | |-+-+-+-+---- typematic rate indicator (see INT 16,3)
	     | | | | | `------- A in period formula (see below)
	     | | | `---------- B is period formula (see below)
	     | `------------- typematic delay
	     `-------------- always zero

	    delay = (rate+1) * 250   (in milliseconds)
	    rate = (8+A) * (2**B) * 4.17  (in seconds,  20%)

	    Defaults to 10.9 characters per second and a 500ms delay.  If a
	    command byte (byte with high bit set) is received instead of an
	    option byte this command is cancelled.
	F4  Enable Keyboard, cause the keyboard to clear its output buffer
	    and last typematic key and then respond with an ACK.  The
	    keyboard then begins scanning.
	F5  Default w/Disable, resets keyboard to power-on condition by
	    clearing the output buffer, resetting typematic rate/delay,
	    resetting last typematic key and setting default key types.
	    The keyboard responds with an ACK and waits for the next
	    instruction.
	F6  Set Default, resets to power-on condition by clearing the output
	    buffer, resetting typematic rate/delay and last typematic key
	    and sets default key types.  The keyboard responds with an ACK
	    and continues scanning.
	F7  PS/2 Set All Keys to Typematic, keyboard responds by sending an
	    ACK, clearing its output buffer and setting the key type to
	    Typematic.	 Scanning continues if scanning was enabled.  This
	    command may be sent while using any Scan Code Set but only has
	    effect when Scan Code Set 3 is in use.
	F8  PS/2 Set All Keys to Make/Break, keyboard responds by sending an
	    ACK, clearing its output buffer and setting the key type to
	    Make/Break.  Scanning continues if scanning was enabled.  This
	    command may be sent while using any Scan Code Set but only has
	    effect when Scan Code Set 3 is in use.
	F9  PS/2 Set All Keys to Make, keyboard responds by sending an ACK,
	    clearing its output buffer and setting the key type to Make.
	    Scanning continues if scanning was enabled.  This command may
	    be sent while using any Scan Code Set but only has effect when
	    Scan Code Set 3 is in use.
	FA  PS/2 Set All Keys to Typematic Make/Break, keyboard responds by
	    sending an ACK, clearing its output buffer and setting the key
	    type to Typematic Make/Break.  Scanning continues if scanning
	    was enabled.  This command may be sent while using any Scan Code
	    Set but only has effect when Scan Code Set 3 is in use.
	FB  PS/2 Set Key Type to Typematic, keyboard responds by sending an
	    ACK, clearing its output buffer and then waiting for the key ID
	    (make code from Scan Code Set 3).  The specified key type is then
	    set to typematic.	This command may be sent while using any
	    Scan Code Set but only has effect when Scan Code Set 3 is in use.
	FC  PS/2 Set Key Type to Make/Break, keyboard responds by sending an
	    ACK, clearing its output buffer and then waiting for the key ID
	    (make code from Scan Code Set 3).  The specified key type is then
	    set to Make/Break.	 This command may be sent while using any Scan
	    Code Set but only has effect when Scan Code Set 3 is in use.
	FD  PS/2 Set Key Type to Make, keyboard responds by sending an ACK,
	    clearing its output buffer and then waiting for the key ID (make
	    code from Scan Code Set 3).  The specified key type is then set
	    to Make.  This command may be sent while using any Scan Code Set
	    but only has effect when Scan Code Set 3 is in use.
	FE  Resend, should be sent when a transmission error is detected
	    from the keyboard
	FF  Reset, Keyboard sends ACK and waits for system to receive it
	    then begins a program reset and Basic Assurance Test (BAT).
	    Keyboard returns a one byte completion code then sets default
	    Scan Code Set 2.


Keyboard Responses to System (via 8042 port 60h)


	00  Key Detection Error or Overrun Error for Scan Code Set 1,
	    replaces last key in the keyboard buffer if the buffer is full. 
	AA  BAT Completion Code, keyboard sends this to indicate the keyboard
	    test was successful.
	EE  Echo Response, response to the Echo command.
	F0  Break Code Prefix in Scan Code Sets 2 and 3.
	FA  Acknowledge, keyboard sends this whenever a valid command or
	    data byte is received (except on Echo and Resend commands).
	FC  BAT Failure Code, keyboard sends this to indicate the keyboard
	    test failed and stops scanning until a response or reset is sent.
	FE  Resend, keyboard request resend of data when data sent to it is
	    invalid or arrives with invalid parity.
	FF  Key Detection Error or Overrun Error for Scan Code Set 2 or 3,
	    replaces last key in the keyboard buffer if the buffer is full.
	id  Keyboard ID Response, keyboard sends a two byte ID after ACK'ing
	    the Read ID command.  The byte stream contains 83AB in LSB, MSB
	    order.  The keyboard then resumes scanning.


	- command F7 through FD are NOP's on the AT and are ACK'ed but not
	  acted upon
	- see	8042  MAKE CODES  BREAK CODES  INT 16,3