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Introduction
Code 39 (also known as USS Code 39, Code three of nine) is the
first alpha-numeric symbology developed to be used in non-retail
environment. It is widely used to code alphanumeric information,
such as the model number etc.
Code39 is designed to encode 26 upper case letters, 10 digits and 7
special characters:
A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T,
U, V, W, X, Y, Z
0, 1, 2, 3, 4, 5, 6, 7, 8, 9
-, ., *, $, /, +, %, SPACE.
It Is called code 39 or three of nine because each character
encoded is made up of 5 bars and 4 spaces for a total of 9 elements
and 3 out of 9 element are always wide.
A complete code 39 barcode must include a start character * and a
stop character *. In this way code 39 is self-checking.
The height of the bars must be at least 0.15 times of the
symbol¨s length or 0.25 inches, whichever is larger.
Code 39 is a discrete symbology. Two adjacent characters are
separated by an inter-character gap. To have the good barcode
quality, the width of the inter-character gap usually equals to the
width of the narrowest element, called X.
Code39 requires a starting quiet zone with the minimum 10 times
of X dimension or 0.10 inch whichever is greater. The same width
requirement applies to the trailing quiet zone.
Variants
Code 39 Mod 43 - In applications that require very high level
of accuracy a modulo 43 check sum digit is appended to the last
character. Also known as HIBC and LOGMARS.
Code 39 Extended - this encoding variant allows the full ASCII
table, 128 characters to be encoded.
Structure of a code 39 barcode
A typical code 39 barcode has the following structure:
- A start character - the asterisk(*)
- Message encoded
- A stop character - the second asterisk(*)
Check Digit Calculation
To calculate the optional checksum digit, follow the following
steps.
| CODE39
CHAR TABLE |
| Ch |
Val |
Ch |
Val |
Ch |
val |
ch |
Val |
| 0 |
0 |
A |
10 |
N |
23 |
- |
36 |
| 1 |
1 |
B |
11 |
O |
24 |
. |
37 |
| 2 |
2 |
C |
12 |
P |
25 |
sp |
38 |
| 3 |
3 |
D |
13 |
Q |
26 |
$ |
39 |
| 4 |
4 |
E |
14 |
R |
27 |
/ |
40 |
| 5 |
5 |
F |
14 |
S |
28 |
+ |
41 |
| 6 |
6 |
G |
16 |
T |
29 |
% |
42 |
| 7 |
7 |
H |
17 |
U |
30 |
|
|
| 8 |
8 |
I |
18 |
V |
31 |
|
|
| 9 |
9 |
J |
19 |
W |
32 |
|
|
| |
|
K |
20 |
X |
33 |
|
|
| |
|
L |
21 |
Y |
34 |
|
|
| |
|
M |
22 |
Z |
35 |
|
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- Take the value (0 through 42) of each character in the
barcode. The start and stop characters are not included in the
checksum calculation.
- Sum the value of each of the values of each of the characters
described in step 1.
- Divide the result from step 2 by 43.
- The remainder from the division in step 3 is the checksum
character that will be appended to the data message before the
stop character.
Code 39 Extended
The code 39 symbology can be extended to encode all 128
characters in the ASCII table. In the full ASCII mode, the symbols $
/ % and + are used as precedence codes with the 26 letters as shown
below. Since the same symbol now can be interpreted as one character
in Extended Code 39 mode and two characters in Code 39 mode, the
readers must be set to extended mode to read the data correctly. We
listed the mapping chart at the left. Code39 extended is sometimes
called Code39 Full ASCII.
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