The communication is running through two wires. In fact it is serial synchronous communication, where the wire called DATA (pin 2) serves for data transfer and the wire CLOCK (pin 1) provides clock signal. The power supply voltage 5V is on pin number 5, ground GND is on pin 4 and RESET signal is on pin 3. The RESET signal is used due to compatibility with an old type of XT keyboard. The frequency of CLOCK signal can vary from 10kHz to 20kHz.
After pressing a key the keyboard sends a key code to the PC. After releasing
a release-code is sent out followed by the key code of released key.
s--DATA--PS
s = start bit
DATA = first bit (LSB least significant bit)
P = parity bit (odd parity)
S = stop bit
As an example is shown the code of key 'A' (0x1C):
parity bit
|
start bit |
| |
00011100001
|
stop bit
In case of communication from computer to keyboard the computer starts with setting the DATA wire to state L and the keyboard will answer with the clock pulses on the CLOCK wire. The computer follows clock signal and sends all start, data, parity and stop bits like during communication from the keyboard to the computer.
(all control codes are in hexadecimal format)
0xFF - reset of keyboard - runs the power-on test
0xFE - request of the last sent key code from keyboard
0xFA - acknowledge - ACK
0xF6 - retrieving of implicit setting
0xF5 - implicit blocking of keyboard - forces keyboard reset,
returns code ACK (0xFA), interrupts of keyboard scanning
and waits for next command, has no influence on LED indicators
0xF4 - keyboard deblocking - resets output buffer, deblocks keyboard
and returns code ACK (0xFA)
0xEE - echo - keyboard answers back with the code 0xEE too - just for test
0xF2 - reading keyboard ID - keyboard answers ACK with two ID bytes
(0x83,0xAB) and continues in keyboard scanning
0xED - control code of keyboard LED indicator
b0 - Scrollock - 1 on/0 off
b1 - Numlock - 1 on/0 off
b2 - Capslock - 1 on/0 off
b3..b7 - 0
(all control codes are in hexadecimal format)
0xFF - output buffer overflow - keyboard detects an error
0xFE - request of the last sent key code from the computer, bad code,
command, parity etc.
0xFA - acknowledge - ACK
0xF0 k - releasing of a key - k -> code of released key
0xAA - successful power-on test
0xEE - echo - computer answers back with the code 0xEE too - just for test
0x00 - output buffer overflow - keyboard detects an error
** Main keys **
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Key output code when pressing output code when releasing
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` 0x0E 0xF0 0x0E
1 0x16 0xF0 0x16
2 0x1E 0xF0 0x1E
3 0x26 0xF0 0x26
4 0x25 0xF0 0x25
5 0x2E 0xF0 0x2E
6 0x36 0xF0 0x36
7 0x3D 0xF0 0x3D
8 0x3E 0xF0 0x3E
9 0x46 0xF0 0x46
0 0x45 0xF0 0x45
- 0x4E 0xF0 0x4E
= 0x55 0xF0 0x55
Backspace 0x66 0xF0 0x66
Tab key 0x0D 0xF0 0x0D
Q 0x15 0xF0 0x15
W 0x1D 0xF0 0x1D
E 0x24 0xF0 0x24
R 0x2D 0xF0 0x2D
T 0x2C 0xF0 0x2C
Y 0x35 0xF0 0x35
U 0x3C 0xF0 0x3C
I 0x43 0xF0 0x43
O 0x44 0xF0 0x44
P 0x4D 0xF0 0x4D
[ 0x54 0xF0 0x54
] 0x5B 0xF0 0x5B
\ 0x5D 0xF0 0x5D
Caps Lock 0x58 0xF0 0x58
A 0x1C 0xF0 0x1C
S 0x1B 0xF0 0x1B
D 0x23 0xF0 0x23
F 0x2B 0xF0 0x2B
G 0x34 0xF0 0x34
H 0x33 0xF0 0x33
J 0x3B 0xF0 0x3B
K 0x42 0xF0 0x42
L 0x4B 0xF0 0x4B
; 0x4C 0xF0 0x4C
' 0x52 0xF0 0x52
Enter 0x5A 0xF0 0x5A
Left Shift 0x12 0xF0 0x12
Z 0x1A 0xF0 0x1A
X 0x22 0xF0 0x22
C 0x21 0xF0 0x21
V 0x2A 0xF0 0x2A
B 0x32 0xF0 0x32
N 0x31 0xF0 0x31
M 0x3A 0xF0 0x3A
, 0x41 0xF0 0x41
. 0x49 0xF0 0x49
/ 0x4A 0xF0 0x4A
Right Shift 0x59 0xF0 0x59
Left Ctrl 0x14 0xF0 0x14
Left Alt 0x11 0xF0 0x11
Space 0x29 0xF0 0x29
Right Alt 0xE0 0x11 0xE0 0xF0 0x11
Right Ctrl 0xE0 0x14 0xE0 0xF0 0x14
ESC 0x76 0xF0 0x76
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** Functions keys **
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Key output code when pressing output code when releasing
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F1 0x05 0xF0 0x05
F2 0x06 0xF0 0x06
F3 0x04 0xF0 0x04
F4 0x0C 0xF0 0x0C
F5 0x03 0xF0 0x03
F6 0x0B 0xF0 0x0B
F7 0x83 0xF0 0x83
F8 0x0A 0xF0 0x0A
F9 0x01 0xF0 0x01
F10 0x09 0xF0 0x09
F11 0x78 0xF0 0x78
F12 0x07 0xF0 0x07
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** Numeric keys **
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Key output code when pressing output code when releasing
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NumLock 0x77 0xF0 0x77
- 0x7B 0xF0 0x7B
/ 0xE0 0x4A 0xE0 0xF0 0x4A Note 1,2
. 0x71 0xF0 0x71
* 0x7C 0xF0 0x7C
+ 0x79 0xF0 0x79
Enter 0xE0 0x5A 0xE0 0xF0 0x5A
0 0x70 0xF0 0x70
1 0x69 0xF0 0x69
2 0x72 0xF0 0x72
3 0x7A 0xF0 0x7A
4 0x6B 0xF0 0x6B
5 0x73 0xF0 0x73
6 0x74 0xF0 0x74
7 0x6C 0xF0 0x6C
8 0x75 0xF0 0x75
9 0x7D 0xF0 0x7D
-----------------------------------------------------------------------
** Extended part **
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Key output code when pressing output code when releasing
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Ins 0xE0 0x70 0xE0 0xF0 0x70 Note 1,2,3
Home 0xE0 0x6C 0xE0 0xF0 0x6C Note 1,2,3
Pg Up 0xE0 0x7D 0xE0 0xF0 0x7D Note 1,2,3
Del 0xE0 0x71 0xE0 0xF0 0x71 Note 1,2,3
End 0xE0 0x69 0xE0 0xF0 0x69 Note 1,2,3
Pg Dn 0xE0 0x7A 0xE0 0xF0 0x7A Note 1,2,3
Up arrow 0xE0 0x75 0xE0 0xF0 0x75 Note 1,2,3
Left arrow 0xE0 0x6B 0xE0 0xF0 0x6B Note 1,2,3
Right arrow 0xE0 0x74 0xE0 0xF0 0x74 Note 1,2,3
Down arrow 0xE0 0x72 0xE0 0xF0 0x72 Note 1,2,3
PrtSc 0xE0 0x12 0xE0 0x7C 0xE0 0xF0 0x7C 0xE0 0xF0 0x12
Ctl-PrtSc 0xE0 0x7C 0xE0 0xF0 0x7C
Alt-PrtSc 0x84 0xE0 0x84
ScrLk 0x7E 0xF0 0x7E
Ctrl-Break 0xE0 0x7E 0xE0 0xF0 0x7E nothing
-----------------------------------------------------------------------
** Notes **
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Note 1
When the left shift key is pressed :
Output code when pressing - 0xE0 0xF0 0x12 0x** 0x**
Output code when releasing - 0x** 0x** 0x** 0xE0 0x12
Note 2
When the right shift key is pressed :
Output code when pressing - 0xE0 0xF0 0x59 0x** 0x**
Output code when releasing - 0x** 0x** 0x** 0xE0 0x59
Note 3
When the Num Lock key is pressed :
Output code when pressing - 0xE0 0x12 0x** 0x**
Output code when releasing - 0x** 0x** 0x** 0xE0 0xF0 0x12
'0x** 0x**' - normal output code when pressing key
'0x** 0x** 0x**' - normal output code when releasing key
Daniel Prokopec, email.: prokopec@login.cz
Větrná 678/IV. Vysoké Mýto 56601
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