Code 128

A Swiss postal barcode encoding "RI 476 394 652 CH" in Code 128-B

Code 128 is 7494122205787105a very high-density barcode symbology. It is used for alphanumeric or numeric-only barcodes. It can encode all 128 characters of ASCII and, by use of an extension character (FNC4), the Latin-1 characters defined in ISO/IEC 8859-1.

GS1-128 (formerly known as UCC/EAN-128) is a subset of Code 128 and is used extensively worldwide in shipping and packaging industries as a product identification code for the container and pallet levels in the supply chain. The symbology was formerly defined as ISO/IEC 15417:2007.

Specification

"Code 128 sections"
Code 128 sections. 1. Quiet zone, 2. Start/stop character, 3. Encoded data, 4. Check character

A Code 128 barcode will have six sections:

  1. Quiet zone
  2. Start character
  3. Encoded data
  4. Check character
  5. Stop character
  6. Quiet zone

The check character is calculated from a weighted sum (modulo 103) of all the characters.

Subtypes

Code 128 includes 108 symbols: 103 data symbols, 3 start symbols, and 2 stop symbols. The symbols consist of three black bars and three white spaces of varying widths. Each bar width is 1 to 4 modules (a module is a unit width) wide. All but the stop symbol are fixed width: the sum of the widths of the three black bars and three white bars is fixed.

The stop pattern is composed of two overlapped symbols and has four bars. The stop pattern permits bidirectional scanning. When the stop pattern is read left-to-right (the usual case), the stop symbol is recognized. When the stop pattern is read right-to-left, the reverse stop symbol is recognized. A scanner seeing the reverse stop symbol then knows it must read the symbol in reverse.

Despite its name, Code 128 does not have 128 distinct symbols, so it cannot represent 128 code-points directly. To represent all 128 ASCII values, it shifts among three code sets (A, B, C). Together, code sets A and B cover all 128 ASCII characters. Code set C is used to efficiently encode digit strings. The initial subset is selected by using the appropriate start symbol. Within each code set, some of the 103 data code points are reserved for shifting to one of the other two code sets. The shifts are done using code points 98 and 99 in code sets A and B, 100 in code sets A and C and 101 in code sets B and C to switch between them):

Quiet zone

The minimum width of the Quiet Zone to the left and right of the 128 Bar Code is 10x, where x is the minimum width of a module. It is mandatory at the left and right side of the barcode. The quiet zone must not be less than 4 mm × 1.65 mm depending on the type of bar code. Source: Figure 5.2.1.4.4 – 1 of GS1 General Specifications

Start/stop and encoded data

Each character in the barcode symbol is composed of three bars and three spaces except for the stop character, which adds an additional extra bar of length 2. Each bar or space is 1, 2, 3 or 4 units wide, the sum of the widths of bars must be even (4, 6 or 8 units), the sum of the widths of the spaces must be odd (3, 5 or 7 units), and total 11 units per character. For instance, encoding the ASCII character "0" can be viewed as 10011101100, where a 1 is a bar and a 0 is a space. A single 1 would be the thinnest line in the bar code. Three 1s in sequence (111) indicates a bar three times as thick as a single 1 bar.

The code uses 107 of the 108 possible patterns that fulfill the required criteria, with the pattern 211133 deliberately remaining unused. This is done to enhance omnidirectional scanning and help prevent misreads (if 211133 represented a legitimate symbol it could be mistaken for the stop code 2331112 when scanned backwards).

Check digit calculation

The check digit is a weighted modulo-103 checksum. It is calculated by summing the start code 'value' to the products of each character's 'value' multiplied by its position in the barcode string. The start character and first encoded value are in position 1. The sum of the products is then reduced modulo 103. The remainder is then converted back to one of the 103 non-delimiter characters (following the instructions given below) and appended to the barcode, immediately before the stop character.

For example, in the following table, the code 128 variant A checksum value is calculated for the alphanumeric string PJJ123C:

Code Value Position Value ×
Position
Start Code A 103 1 103
P 48 1 48
J 42 2 84
J 42 3 126
1 17 4 68
2 18 5 90
3 19 6 114
C 35 7 245
Sum 878
Remainder mod 103 54

Calculating check digit with multiple variants

As Code 128 allows multiple variants, as well as switching between variants within a single barcode, the absolute Code 128 value of a character is completely independent of its value within a given variant. For instance the Variant C value "33" and the Variant B value "A" are both considered to be a Code 128 value of 33, and the check digit would be computed based on the value of 33 times the character's position within the barcode.

Using FNC4 to encode high (128–255) characters

Function 4 (FNC4) can be used to encode all the LATIN-1 (ISO-8859-1) characters in a Code 128 barcode.[1] The feature is not widely supported and is not used in GS128.[2][3] When a single FNC4 is present in a string, the following character will be converted to ASCII as usual (character sets A and B) and then have 128 added to the ASCII value. (If the following symbol is a shift, then a second symbol will be used to obtain the character.) If two FNC4s are used consecutively then all following characters will be treated as such, up to the end of the string or another pair of FNC4s. Between the double FNC4s, a single FNC4 will be used to denote that the following character will be standard ASCII.[4]

Bar code widths

Code128 specifies a combination of 6 bars and spaces for each character except the Stop character, which uses 7. Thus, each character begins with a bar and ends with a space (with the exception of the stop character, which ends in a bar). The following tables detail the widths associated with each bar and space for each character. The width of each bar or space can be 1, 2, 3 or 4 units (modules). Using the example above, an 'A' would be depicted with the pattern 10100011000, or as 111323 in the tables below.

Code 128
Value 128A 128B 128C ASCII Code (Common/Barcodesoft) Character (Common/Barcodesoft) Bar/Space Pattern Bar/Space Weights
0 space space 00 0032 or 0212 / 252 Space or Ô / ü 11011001100 212222
1 ! ! 01 33 ! 11001101100 222122
2 " " 02 34 " 11001100110 222221
3 # # 03 35 # 10010011000 121223
4 $ $ 04 36 $ 10010001100 121322
5 % % 05 37 % 10001001100 131222
6 & & 06 38 & 10011001000 122213
7 ' ' 07 39 ' 10011000100 122312
8 ( ( 08 40 ( 10001100100 132212
9 ) ) 09 41 ) 11001001000 221213
10 * * 10 42 * 11001000100 221312
11 + + 11 43 + 11000100100 231212
12 , , 12 44 , 10110011100 112232
13 - - 13 45 - 10011011100 122132
14 . . 14 46 . 10011001110 122231
15 / / 15 47 / 10111001100 113222
16 0 0 16 48 0 10011101100 123122
17 1 1 17 49 1 10011100110 123221
18 2 2 18 50 2 11001110010 223211
19 3 3 19 51 3 11001011100 221132
20 4 4 20 52 4 11001001110 221231
21 5 5 21 53 5 11011100100 213212
22 6 6 22 54 6 11001110100 223112
23 7 7 23 55 7 11101101110 312131
24 8 8 24 56 8 11101001100 311222
25 9 9 25 57 9 11100101100 321122
26  :  : 26 58  : 11100100110 321221
27 ; ; 27 59 ; 11101100100 312212
28 < < 28 60 < 11100110100 322112
29 = = 29 61 = 11100110010 322211
30 > > 30 62 > 11011011000 212123
31 ? ? 31 63 ? 11011000110 212321
32 @ @ 32 64 @ 11000110110 232121
33 A A 33 65 A 10100011000 111323
34 B B 34 66 B 10001011000 131123
35 C C 35 67 C 10001000110 131321
36 D D 36 68 D 10110001000 112313
37 E E 37 69 E 10001101000 132113
38 F F 38 70 F 10001100010 132311
39 G G 39 71 G 11010001000 211313
40 H H 40 72 H 11000101000 231113
41 I I 41 73 I 11000100010 231311
42 J J 42 74 J 10110111000 112133
43 K K 43 75 K 10110001110 112331
44 L L 44 76 L 10001101110 132131
45 M M 45 77 M 10111011000 113123
46 N N 46 78 N 10111000110 113321
47 O O 47 79 O 10001110110 133121
48 P P 48 80 P 11101110110 313121
49 Q Q 49 81 Q 11010001110 211331
50 R R 50 82 R 11000101110 231131
51 S S 51 83 S 11011101000 213113
52 T T 52 84 T 11011100010 213311
53 U U 53 85 U 11011101110 213131
54 V V 54 86 V 11101011000 311123
55 W W 55 87 W 11101000110 311321
56 X X 56 88 X 11100010110 331121
57 Y Y 57 89 Y 11101101000 312113
58 Z Z 58 90 Z 11101100010 312311
59 [ [ 59 91 [ 11100011010 332111
60 \ \ 60 92 \ 11101111010 314111
61 ] ] 61 93 ] 11001000010 221411
62 ^ ^ 62 94 ^ 11110001010 431111
63 _ _ 63 95 _ 10100110000 111224
64 NUL ` 64 96 ` 10100001100 111422
65 SOH a 65 97 a 10010110000 121124
66 STX b 66 98 b 10010000110 121421
67 ETX c 67 99 c 10000101100 141122
68 EOT d 68 100 d 10000100110 141221
69 ENQ e 69 101 e 10110010000 112214
70 ACK f 70 102 f 10110000100 112412
71 BEL g 71 103 g 10011010000 122114
72 BS h 72 104 h 10011000010 122411
73 HT i 73 105 i 10000110100 142112
74 LF j 74 106 j 10000110010 142211
75 VT k 75 107 k 11000010010 241211
76 FF l 76 108 l 11001010000 221114
77 CR m 77 109 m 11110111010 413111
78 SO n 78 110 n 11000010100 241112
79 SI o 79 111 o 10001111010 134111
80 DLE p 80 112 p 10100111100 111242
81 DC1 q 81 113 q 10010111100 121142
82 DC2 r 82 114 r 10010011110 121241
83 DC3 s 83 115 s 10111100100 114212
84 DC4 t 84 116 t 10011110100 124112
85 NAK u 85 117 u 10011110010 124211
86 SYN v 86 118 v 11110100100 411212
87 ETB w 87 119 w 11110010100 421112
88 CAN x 88 120 x 11110010010 421211
89 EM y 89 121 y 11011011110 212141
90 SUB z 90 122 z 11011110110 214121
91 ESC { 91 123 { 11110110110 412121
92 FS | 92 124 | 10101111000 111143
93 GS } 93 125 } 10100011110 111341
94 RS ~ 94 126 ~ 10001011110 131141
95 US DEL 95 200 / 240 È / ð 10111101000 114113
96 FNC 3 FNC 3 96 201 / 241 É / ñ 10111100010 114311
97 FNC 2 FNC 2 97 202 / 242 Ê / ò 11110101000 411113
98 Shift B Shift A 98 203 / 243 Ë / ó 11110100010 411311
99 Code C Code C 99 204 / 244 Ì / ô 10111011110 113141
100 Code B FNC 4 Code B 205 / 245 Í / õ 10111101110 114131
101 FNC 4 Code A Code A 206 / 246 Î / ö 11101011110 311141
102 FNC 1 FNC 1 FNC 1 207 / 247 Ï / ÷ 11110101110 411131
103 Start Code A 208 / 248 Ð / ø 11010000100 211412
104 Start Code B 209 / 249 Ñ / ù 11010010000 211214
105 Start Code C 210 / 250 Ò / ú 11010011100 211232
106 Stop (7 bars/spaces) 211 / 251 Ó / û 1100011101011 2331112
— Reverse Stop
used to detect reading right to left		 — — 11010111000 211133

The "Code A", "Code B" and "Code C" symbols cause all future symbols to be interpreted according to the corresponding subcode. The "Shift" symbol switches a single following symbol's interpretation between subcodes A and B.

The encoded ASCII char depends on the actual used barcode-font. Especially the ASCII char of value 0 and of value 95 and above can be defined differently in the font that is installed.

The FNCx codes are used for special purposes. FNC1 at the beginning of a bar code indicates that it begins with a 2- 3- or 4-digit application identifier assigned by the Uniform Code Council, which explains the following digits. For example, application identifier 421 indicates that an ISO 3166-1 numeric country code and ship-to postal code follows. For example, the U.S. ZIP code for the White House would generally be printed as "(421) 840 20500", but would actually be coded as "[Start C] [FNC1] 42 18 40 20 50 [Code A] 0 [Check symbol 92] [Stop]"

Check digit calculation for the above Zip code example:

Value Weight Weight × Value
Start C 105 1 105
FNC1 102 1 102
42 42 2 84
18 18 3 54
40 40 4 160
20 20 5 100
50 50 6 300
Code A 101 7 707
0 16 8 128
Sum = 1740
1740 Mod 103 = 92

Availability

For the end user, Code 128 barcodes may be generated by either an outside application to create an image of the barcode, or by a font-based barcode solution. Either solution requires the use of an application or an application add in to calculate the check digit and create the barcode.

Barcode length optimization

Although code set C uses one code symbol to represent two digits, its usage does not necessarily make a more compact code compared to code sets A or B. While encoding "X00Y" with code set A or B results in 7 code symbols (e.g., [Start B] 56 16 16 57 [checksum] [Stop]), encoding the inner "00" with code set C will result in a code 8 symbols long due to the overhead in switching in and out of code set C. Although one symbol is saved on encoding "00" to code symbol C, two code set switching symbols are required: the first to switch into code set C and the second to switch back to code set A or B (e.g., [Start B] 56 [Code C] 00 [Code B] 57 [checksum] [Stop]).

Conversely, applying of code set C to a sequence of digits produces code with fewer symbols compared to code sets A or B only under these conditions:

Position of sequence of digits in data Number of digits for switching to code set C
beginning of data 4+
end of data 4+
middle of data (surrounded by characters from code set A or B) 6+
entire data either 2 or 4+

Example: For data "098x1234567y23", savings on barcode length using code set C are achieved only if it is applied to middle part of data and the transition to code set C is done when there are an even number of digits remaining to encode (so "234567"). For beginning and ending part of the code, switching to code set C is not effective. Code symbols: [Start B] 16 25 24 88 17 [Code C] 23 45 67 [Code B] 89 18 19 [checksum] [Stop].

Delaying the transition to code set C until there are an even number of digits remaining avoids an extra symbol. Consider the string "...01234": a delayed switch produces ... 0 [Code C] 12 34 [checksum] [Stop] but an early switch produces ... [Code C] 01 23 [Code A] 4 [checksum] [Stop].[5]

Optimizing length of resulting barcode is important where barcode readers are used which require to detect the entire barcode image at once in order to read a barcode, such as laser scanners. The longer the barcode is, the greater distance of laser barcode reader from barcode image is needed, making reading difficult or impossible above some threshold lengths/distances.

References

  1. ↑ Apparently ISO 15417 Annex F
  2. ↑ Softmatic, http://www.softmatic.com/barcode-code-128.html, stating, "In principle non-ASCII characters like German umlauts (e.g. ÄÖÜ) can be encoded in a Code 128 symbol by using a special character (FNC4). However, this feature is not widely supported. Using a 2D barcode symbology like Aztec or Datamatrix with dedicated support for non-ASCII data might be a better choice."
  3. ↑ GS1 General Specifications (January 2006 – Version 7.0), section 5.3.1.1 GS1-128 Symbology Characteristics, stating, "Characters with ASCII values 128 to 255 may also be encoded in Code 128 Symbols. Characters with ASCII values 128 to 255 accessed by Function 4 Character (FNC4) are reserved for future use and are not used in GS1-128 Bar Code Symbols."
  4. ↑ http://www.han-soft.com/releases/barcode1d/documents/b_code128.html stating, "If a single "FNC 4" character is used, indicates the following data character in the symbol is a extended ASCII character. A "SHIFT" character may follow the "FNC 4" character if it is necessary to change character subset for the following data character. Subsequent data characters revert to the standard ASCII character set. If two consecutive "FNC4" characters are used, all following data characters are extended ASCII characters until two further consecutive "FNC4" characters are encountered or the end of the symbol is reached. If during this sequence of extended encodation a single "FNC4" character is encountered it is used to revert to standard ASCII encodation for the next data character only. "SHIFT" and character subset characters shall have their normal effect during such a sequence."
  5. ↑ GS1 General Specifications, Version 13, Issue 1, Jan-2013, Section 5.4.7.7. Use of Start, Code Set, and Shift Characters to Minimize Symbol Length (Informative), pages 268 to 269. This section gives the compression strategy.

External links

Sample code

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