PC Keyboard Scan Codes

Altek Instruments have designed and built a general purpose, low cost PC interface which generates Keyboard Scancodes. Any key or combination of keys may be emulated thus enabling any applications program to interact with RS232 peripheral devices. We call it The Mule (TM).

Altek Instruments Ltd have a range of products designed for the data collection/automatic ID industries.

Overview

The PC keyboard interface is designed so the system software has maximum flexibility in defining certain keyboard operations. This is accomplished by having the keyboard return scancodes rather than ASCII codes. Each key generates a 'make' scancode when pressed and a 'break' scancode when released. The computer system interprets the scancodes to determine what operation it is to perform. For historical compatibility reasons computers can employ different sets of scancodes for different purposes. Earlier PC computers tend to use the XT scancode set. Current PC computers tend to use the AT scancode set. The MF1, MF2 and MF3 sets are alternatives, similar in many respects to the XT and AT sets. The table below shows the scancodes generated when a key is pressed- the 'make' code. The 'break' code may be derived from the 'make' code as described later. Notice that scancodes may consist of a single or several bytes.

Many keyboard scancode tables published are not completely accurate. Confusion arises between scancodes issued by the keyboard hardware and the scancodes appearing in the keyboard buffer. The scancodes presented here are those actually sent by the keyboard hardware. The computer BIOS may translate the code for compatibility reasons. For example, the XT scancode set was first used in the original IBM PC computer. Other IBM computers and terminals used a different scancode set. Apparently IBM tried to bring the PC into line with its other products when the IBM PC/AT was launched. The keyboard for that machine used a scancode set virtually identical to other IBM machines. However to maintain compatibility with earlier PC software the BIOS for the AT machines converted the AT scancodes into the earlier XT scancodes. At the current time (June 1995) this system of code conversion in the BIOS persists. The code you read from the keyboard buffer is not necessarily the same code transmitted from the keyboard.

How to Calculate the Scancode

  1. Use the keyboard sketches to determine the 'Key Number'. Note that the 102 key keyboard shown is the keyboard used in the UK. In the USA and some other countries a 101 key keyboard is used- there are minor scancode differences- read the table notes.
  2. Lookup the 'Key number' in the table and read of the 'Make'scancode. Note that the scancode differs depending on the scancode set currently in use. Note also that some scancodes consist of more than 1 byte.
  3. Calculate the 'break' scancode as detailed below

'Break' scancodes for PC/XT computers

The 'break' code for XT style computers is the 'Make' code OR'd with the hexadecimal value 80. (If you are unfamiliar with hexadecimal numbers then simply change the first character of the scancode thus: Change 0 to 8, 1 to 9, 2 to A, 3 to B, 4 to C, 5 to D, 6 to E, 7 to F)

For example the scancodes generated by pressing and releasing the Escape key (Key Number 110) are 01 81

'Break' scancodes for PC/AT computers

Most PC's made since about 1989 use keyboards that generate AT scancodes (Though the codes may be converted to XT scancodes in the BIOS). The 'break' code for AT class scancodes is simply the 'make' code preceded by hex F0. For example the scancodes generated when the Escape key is pressed and released are 76 F0 76.

Special scancodes of potential interest to Altek Mule(tm) users

If the keyboard's buffer overflows it sends a special scancode to the computer. This generally causes the computer to sound a warning beep. Altek Mule(tm) users may issue this code if they want to sound the beep to draw the operators attention. For PC computers using XT scancodes the code is hex FF. For computers using AT scancodes the code is 00.

PC Keyboard, 102 key

[Keyboard 102 keys]

PC Keyboard, 84 key

[Keyboard 84 keys]

Scancode Table

Table Notes

Scancode Table
Key Num XT AT MF1 MF2 MF3
1 29 0E 29 0E 0E
2 02 16 02 16 16
3 03 1E 03 1E 1E
4 04 26 04 26 26
5 05 25 05 25 25
6 06 2E 06 2E 2E
7 07 36 07 36 36
8 08 3D 08 3D 3D
9 09 3E 09 3E 3E
10 0A 46 0A 46 46
11 0B 45 0B 45 45
12 0C 4E 0C 4E 4E
13 0D 55 0D 55 55
15 0E 66 0E 66 66
16 0F 0D 0F 0D 0D
17 10 15 10 15 15
18 11 1D 11 1D 1D
19 12 24 12 24 24
20 13 2D 13 2D 2D
21 14 2C 14 2C 2C
22 15 35 15 35 35
23 16 3C 16 3C 3C
24 17 43 17 43 43
25 18 44 18 44 44
26 19 4D 19 4D 4D
27 1A 54 1A 54 54
28 1B 5B 1B 5B 5B
* 29 2B 5D 2B 5D 5C
30 3A 58 3A 58 14
31 1E 1C 1E 1C 1C
32 1F 1B 1F 1B 1B
33 20 23 20 23 23
34 21 2B 21 2B 2B
35 22 34 22 34 34
36 23 33 23 33 33
37 24 3B 24 3B 3B
38 25 42 25 42 42
39 26 4B 26 4B 4B
40 27 4C 27 4C 4C
41 28 52 28 52 52
** 42 2B 5D 2B 5D 53
43 1C 5A 1C 5A 5A
44 2A 12 2A 12 12
** 45 56 61 56 61 13
46 2C 1A 2C 1A 1A
47 2D 22 2D 22 22
48 2E 21 2E 21 21
49 2F 2A 2F 2A 2A
50 30 32 30 32 32
51 31 31 31 31 31
52 32 3A 32 3A 3A
53 33 41 33 41 41
54 34 49 34 49 49
55 35 4A 35 4A 4A
57 36 59 36 59 59
58 1D 14 1D 14 11
60 38 11 38 11 19
61 39 29 39 29 29
62 E038 E011 E038 E011 39
64 E01D E014 E01D E014 58
75 E052 E070 E052 E070 67
76 E053 E071 E053 E071 64
79 E04B E06B E04B E06B 61
80 E047 E06C E047 E06C 6E
81 E04F E069 E04F E069 65
83 E048 E075 E048 E075 63
84 E050 E072 E050 E072 60
85 E049 E07D E049 E07D 6F
86 E051 E07A E051 E07A 6D
89 E04D E074 E04D E074 6A
90 45 77 45 77 76
91 47 6C 47 6C 6C
92 4B 6B 4B 6B 6B
93 4F 69 4F 69 69
95 E035 E04A E035 E04A 77
96 48 75 48 75 75
97 4C 73 4C 73 73
98 50 72 50 72 72
99 52 70 52 70 70
100 37 7C 37 7C 7E
101 49 7D 49 7D 7D
102 4D 74 4D 74 74
103 51 7A 51 7A 7A
104 53 71 53 71 71
105 4A 7B 4A 7B 84
106 4E 79 4E 79 7C
108 E01C E05A E01C E05A 79
110 01 76 01 76 08
112 3B 05 3B 05 07
113 3C 06 3C 06 0F
114 3D 04 3D 04 17
115 3E 0C 3E 0C 1F
116 3F 03 3F 03 27
117 40 0B 40 0B 2F
118 41 83 41 83 37
119 42 0A 42 0A 3F
120 43 01 43 01 47
121 44 09 44 09 4F
122 57 78 57 78 56
123 58 07 58 07 5E
124 E02AE037 E012E07C E02AE037 E012E07C 57
125 46 7E 46 7E 5F
126 E11D45E1
9DC5 		1477F014
F077 		E11D45E1
9DC5 		E11477E1
F014F077 		62

Windows 95 Update

The Windows 95 keyboard has 3 extra keys. They are the two 'Flying Windows' keys and the 'Pop Up Menu' key. These keys may be emulated by The Mule in Scancode Mode just like any other key. The appropriate 'make' and 'break' scancodes are shown below...

 

Make

Break

Left Flying Window

E0 1F

 E0 F0 1F

Right Flying Window

E0 27

 E0 F0 27

Pop Up Menu

E0 2F

 E0 F0 2F

Altek Instruments have designed and built a general purpose, low cost PC interface which generates Keyboard Scancodes. Any key or combination of keys may be emulated thus enabling any applications program to interact with RS232 peripheral devices. We call it The Mule (TM).

Altek Instruments Ltd have a range of products designed for the data collection/automatic ID industries.