Code 39, the first alpha-numeric symbology to be developed, is
still widely used-especially in non-retail environments. It is the standard bar
code used by the United States Department of Defense, and is also used by the
Health Industry Bar Code Council (HIBCC). Code 39 is also known as "3 of 9
Code" and "USD-3".
A typical Code 39 bar code is:
Code 39 is a discrete, variable-length symbology. It is
self-checking in that a single print defect cannot transpose one character into
another valid character.
Since Code 39 is
self-checking, a check digit normally isn't necessary. However, in applications
that require an extremely high level of accuracy a modulo 43 checksum digit may
be added.
To
calculate the optional checksum digit, follow the following steps.
- Take the value (0 through 42) of
each character in the bar code. 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.
Once the checksum digit has
been calculated we know the entire message which must be encoded in the bars
and spaces. Continuing with our example, we will encode, from zero, the Code 39
bar code we used in our example above: HI345678 with a
checksum digit of 67.
In the following text, we
will discuss the encoding of the bar code by considering that the number
"1" represents a "dark" or "bar" section of the
bar code whereas a "0" represents a "light" or
"space" section of the bar code. Thus the numbers 1101 represents a
double-wide bar (11), followed by a single-wide space (0), followed by a
single-wide bar (1). This would be printed in the bar code as:
STRUCTURE
OF A CODE 39 BARCODE
A Code 39 bar code has the
following structure:
- A start character - the asterisk
(*) character.
- Any number of characters encoded
from the table below.
- An optional checksum digit calculated
as described above and encoded from the table below.
- A stop character, which is a
second asterisk character.
This table indicates how to
encode each digit of a Code 39 bar code. Note that the "Width
Encoding" column is expressed as "N" for narrow and
"W" for wide while the "Barcode Encoding" column represents
how the bar code will actually be encoded as described above in "Encoding
the Symbol."
Keep in
mind that each character begins and ends with a bar, thus the "bar code encoding"
always starts and ends with a "1".
CHECK
VALUE
|
ASCII
CHAR
|
WIDTH
ENCODING
|
BARCODE
ENCODING
|
CHECK
VALUE
|
ASCII
CHAR
|
WIDTH
ENCODING
|
BARCODE
ENCODING
|
0
|
0
|
NNNWWNWNN
|
101001101101
|
22
|
M
|
WNWNNNNWN
|
110110101001
|
1
|
1
|
WNNWNNNNW
|
110100101011
|
23
|
N
|
NNNNWNNWW
|
101011010011
|
2
|
2
|
NNWWNNNNW
|
101100101011
|
24
|
O
|
WNNNWNNWN
|
110101101001
|
3
|
3
|
WNWWNNNNN
|
110110010101
|
25
|
P
|
NNWNWNNWN
|
101101101001
|
4
|
4
|
NNNWWNNNW
|
101001101011
|
26
|
Q
|
NNNNNNWWW
|
101010110011
|
5
|
5
|
WNNWWNNNN
|
110100110101
|
27
|
R
|
WNNNNNWWN
|
110101011001
|
6
|
6
|
NNWWWNNNN
|
101100110101
|
28
|
S
|
NNWNNNWWN
|
101101011001
|
7
|
7
|
NNNWNNWNW
|
101001011011
|
29
|
T
|
NNNNWNWWN
|
101011011001
|
8
|
8
|
WNNWNNWNN
|
110100101101
|
30
|
U
|
WWNNNNNNW
|
110010101011
|
9
|
9
|
NNWWNNWNN
|
101100101101
|
31
|
V
|
NWWNNNNNW
|
100110101011
|
10
|
A
|
NNWWNNWNN
|
110101001011
|
32
|
W
|
WWWNNNNNN
|
110011010101
|
11
|
B
|
NNWNNWNNW
|
101101001011
|
33
|
X
|
NWNNWNNNW
|
100101101011
|
12
|
C
|
WNWNNWNNN
|
110110100101
|
34
|
Y
|
WWNNWNNNN
|
110010110101
|
13
|
D
|
NNNNWWNNW
|
101011001011
|
35
|
Z
|
NWWNWNNNN
|
100110110101
|
14
|
E
|
WNNNWWNNN
|
110101100101
|
36
|
-
|
NWNNNNWNW
|
100101011011
|
15
|
F
|
NNWNWWNNN
|
101101100101
|
37
|
.
|
WWNNNNWNN
|
110010101101
|
16
|
G
|
NNNNNWWNW
|
101010011011
|
38
|
SPACE
|
NWWNNNWNN
|
100110101101
|
17
|
H
|
WNNNNWWNN
|
110101001101
|
39
|
$
|
NWNWNWNNN
|
100100100101
|
18
|
I
|
NNWNNWWNN
|
101101001101
|
40
|
/
|
NWNWNNNWN
|
100100101001
|
19
|
J
|
NNNNWWWNN
|
101011001101
|
41
|
+
|
NWNNNWNWN
|
100101001001
|
20
|
K
|
WNNNNNNWW
|
110101010011
|
42
|
%
|
NNNWNWNWN
|
101001001001
|
21
|
L
|
NNWNNNNWW
|
101101010011
|
n/a
|
*
|
NWNNWNWNN
|
100101101101
|
If a Code
39 bar code starts with a space, that bar code will be appended to any previous
code 39 bar code in the buffer and the system will wait for additional bar
code(s). If a Code 39 bar code doesn't start with a space, the bar code will be
appended to any previous code 39 bar codes and the entire message will be
delivered to the application.
In other
words, if a code 39 bar code has additional bar codes to follow, it must start
with a space-if the bar code is the last bar code in the message it must not
start with a space.
We will now code the
example we used above, TEST8052. In this case we will not use a
check digit.
- The START character (*): 100101101101.
- The digit "T": enocded
as 101011011001.
- The digit "E": enocded
as 110101100101.
- The digit "S": enocded
as 101101011001.
- The digit "T": enocded
as 101011011001.
- The digit "8": enocded
as 110100101101.
- The digit "0": enocded
as 101001101101.
- The digit "5": enocded
as 110100110101.
- The digit "2": enocded
as 101100101011.
- The STOP character (*): 100101101101.
This is shown in the
following graphical representation where the bar code has been sectioned-off
into areas that reflect each of the 10 components just mentioned.
NOTE: In the
above encoding example note that there is an inter-character space between each
character. This is not listed in the list of 10 components, but there is an
inter-character space between each character. This inter-character space is
represented in the graphic by the white space separating the grey areas.
EXTENDED CODE 39 ENCODING
TABLE
It is possible, using Code 39's "Full ASCII Mode" to
encode all 128 ASCII characters. This is accomplished by using the $, /, %, and
+ symbols as "shift" characters. Those characters combined with the
single character that follows indicate which Full ASCII character is to be
used.
ASCII
|
ENCODING
|
ASCII
|
ENCODING
|
ASCII
|
ENCODING
|
ASCII
|
ENCODING
|
NUL
|
%U
|
SP
|
Space
|
@
|
%V
|
`
|
%W
|
SOH
|
$A
|
!
|
/A
|
A
|
A
|
a
|
+A
|
STX
|
$B
|
"
|
/B
|
B
|
B
|
b
|
+B
|
ETX
|
$C
|
#
|
/C
|
C
|
C
|
c
|
+C
|
EOT
|
$D
|
$
|
/D
|
D
|
D
|
d
|
+D
|
ENQ
|
$E
|
%
|
/E
|
E
|
E
|
e
|
+E
|
ACK
|
$F
|
&
|
/F
|
F
|
F
|
f
|
+F
|
BEL
|
$G
|
'
|
/G
|
G
|
G
|
g
|
+G
|
BS
|
$H
|
(
|
/H
|
H
|
H
|
H
|
H
|
HT
|
$I
|
)
|
/I
|
I
|
I
|
i
|
+I
|
LF
|
$J
|
*
|
/J
|
J
|
J
|
j
|
+J
|
VT
|
$K
|
+
|
/K
|
K
|
K
|
k
|
+K
|
FF
|
$L
|
,
|
/L
|
L
|
L
|
l
|
+L
|
CR
|
$M
|
-
|
-
|
M
|
M
|
m
|
+M
|
SO
|
$N
|
.
|
.
|
N
|
N
|
n
|
+N
|
SI
|
$O
|
/
|
/O
|
O
|
O
|
o
|
+O
|
DLE
|
$P
|
0
|
0
|
P
|
P
|
p
|
+P
|
DC1
|
$Q
|
1
|
1
|
Q
|
Q
|
q
|
+Q
|
DC2
|
$R
|
2
|
2
|
R
|
R
|
r
|
+R
|
DC3
|
$S
|
3
|
3
|
S
|
S
|
s
|
+S
|
DC4
|
$T
|
4
|
4
|
T
|
T
|
t
|
+T
|
NAK
|
$U
|
5
|
5
|
U
|
U
|
u
|
+U
|
SYN
|
$V
|
6
|
6
|
V
|
V
|
v
|
+V
|
ETB
|
$W
|
7
|
7
|
W
|
W
|
w
|
+W
|
CAN
|
$X
|
8
|
8
|
X
|
X
|
x
|
+X
|
EM
|
$Y
|
9
|
9
|
Y
|
Y
|
y
|
+Y
|
SUB
|
$Z
|
:
|
/Z
|
Z
|
Z
|
z
|
+Z
|
ESC
|
%A
|
;
|
%F
|
[
|
%K
|
{
|
%P
|
FS
|
%B
|
<<
|
%G
|
\
|
%L
|
|
|
%Q
|
GS
|
%C
|
=
|
%H
|
]
|
%M
|
}
|
%R
|
RS
|
%D
|
>
|
%I
|
^
|
%N
|
~
|
%S
|
YS
|
%E
|
?
|
%J
|
_
|
%O
|
DEL
|
%T,
%X, %Y, %Z
|
