• Bar Code Rules
• Printing Tips and Tricks
• Special Considerations for Rotated Bar Codes

Bar Code Rules

All rules of bar code symbologies must be followed when printing bar codes. For example, you can't print alpha characters in a numeric-only bar code type; to do so will print an invalid code. Some of the rules for the most commonly used bar code symbologies are listed below.

The Uniform Product Code (UPC) family of codes are typically used for product identification, and include UPCA and UPCE. These are numeric codes only, supporting the characters 0 through 9. All UPC codes start with a number system digit that identifies the type of product being coded, and end with a checksum digit.

UPCA consists of a number system digit, ten numbers for the product identification, and a checksum digit. All Cognitive printers automatically calculate the checksum. The checksum is not printed in the bar code subtext. UPC codes usually have extender bars as shown for the UPCE code below, but Cognitive printers can print UPC codes without extender bars if desired.

UPCE is a six-digit variation of the UPC symbology. It always uses number system zero. You must enter the six numbers of the bar code, but not the number system digit or the checksum. The printer calculates the checksum automatically. The bar code is printed with extender bars and bar code subtext. The bar code subtext shows the system number, the six digits of the bar code, and the checksum digit. Using the minus sign bar code modifier removes the checksum from the bar code subtext.

Numbers coded using the UPCE standard must conform to these rules:

• If the manufacturer's code ends in 000, 100, or 200, the valid product code numbers are 00000 to 00999.
• If the manufacturer's code ends in 300, 400, 500, 600, 700, 800, or 900, the valid product code numbers are 00000 to 00099.
• If the manufacturer's code ends in 10, 20, 30, 40, 50, 60, 70, 80, or 90, the valid product code numbers are 00000 to 00009.
• If the manufacturer's code does not end in 0, valid product code numbers are 00005 to 00009.

Pinnacle printers will print an error message if UPCE data does not follow these rules. Other Cognitive printers do not force conformity, but users should be aware that improperly coded data may be rejected by UPCE systems.

HIBC is the Health Industry Bar Code standard symbology. It is similar to normal Code 39, except it uses an automatically generated check digit. The check digit does not appear in the bar code subtext.

Code 93 uses start and stop characters and can use two modulo 47 check digits (referred to as C and K). Character C is a modulo 47 sum of the data character values, weighted from right to left with a 1 through 20 sequence. Character K is a modulo 47 sum of all characters, including C, weighted from right to left with a 1 through 15 sequence.

The characters represented by Code 39 are represented in Code 93 as single bar code characters, but all other Code 93 characters are represented by a control character plus another character. You must take this into account when estimating bar code length.

EAN13 has the same number of bars as UPCA. EAN13 encodes a number system character, eleven data digits, and a checksum. You must enter a number system character and eleven data digits. The printer calculates and adds the check digit, but the check digit does not print in the bar code subtext.

EAN8 encodes a number system character, six data digits, and a checksum. The printer calculates and adds the check digit, but the check digit does not print in the bar code subtext.

Postnet is designed for use with the nine digit ZIP + 4 postal code. Each character to be encoded is represented by five bar code elements, with each element being either a short or tall bar followed by a space. The bar and space widths are constant. Postnet uses a start and stop bar and a modulo 10 check digit. Cognitive printers can automatically calculate and add this digit to the code.

MSI is a modified Plessey code that uses two check digits. Cognitive printers automatically calculate and add the check digits to the bar code. Check digits are not printed in the human-readable bar code subtext.

MSI1 is another modified Plessey code that uses one check digit. Again, Cognitive printers automatically calculate and add the check digit. The check digits are not printed in the human-readable bar code subtext.

PDF417 (an abbreviation for Portable Data File 417), originally developed by Symbol Technologies, Inc., is a two-dimensional stacked bar code symbology. It is a highly compact medium for encoding any data representable by the 256 characters of the International Character Set.

The codeword is the basic unit of a PDF417 bar code. All data encoded using PDF417 is first converted to a decimal value between 0 and 928 inclusive, since there are 928 discrete symbols that can be represented by the allowable pattern of bars and spaces in each codeword. The printer converts the raw data to a series of numeric values following rules that provide optimum data compression. PDF417 provides several different rule sets, or modes, for optimum data compression.

PDF417 provides error detection and correction within the bar code block. The thoroughness of the automatic error checking is called the security level of the code. There are eight security levels, numbered 0-8, as shown in Table 1.

As long as the number of unreadable or missing code words in the bar code block is less than the number indicated for the applicable security level, the code may be read without error.

A high security level provides very reliable data encoding. However, the bar code block gets bigger with increasing security, since more codewords are needed to provide the necessary error checking data. Processing speed also increases significantly with increasing security, since more error checking calculations are performed.

Cognitive printers automatically handle most of the decisions and tasks associated with printing PDF417 bar codes. The printer selects the best mode for the data, encodes it, and does all calculations associated with start and stop characters and error-checking.

Code 128A can encode punctuation, the digits 0 through 9, the English alphabet in uppercase only, the standard ASCII control codes, and the special characters shown in Table 2.

Code 128B can encode punctuation, digits 0 through 9, the English alphabet in both upper and lowercase, and the special characters shown in Table 2.

Code 128C is numeric only, and encodes numbers 00 through 99 plus the special characters shown in Table 2. It encodes numbers more efficiently than Code 128A or Code 128B, since the numbers are encoded as double digits.

Most Cognitive printers support Code 128 Automode Switching. That is, if you specify Code 128 without the A, B, or C modifier the printer will automatically select and shift among the three symbology versions for optimum data compression. This will produce the smallest possible bar code.

Table 2. CODE128 special characters

2 Digit Code	CODE128A	CODE128B	CODE128C
32	FNC3	FNC3	invalid
33	FNC2	FNC2	invalid
34	SHIFT	SHIFT	invalid
35	CODE C	CODE C	invalid
36	CODE B	FNC4	CODE B
37	FNC4	CODE A	CODE A
38	FNC1	FNC1	FNC1

Bar Code Printing Tips & Tricks

Many factors can affect bar code reliability, and the bar code printer does not control all of them. The printer programmer and user must assume responsibility for some aspects of bar code printing. Improper programming or improper printer use can produce bar codes that will not scan reliably.

Common errors resulting in unscannable or unreliable bar codes include:

1. Using a bar code symbology that is incompatible with the encoded data.
2. Trying to read a bar code with a scanner that will not accept the bar code symbology being used. (Remember, the bar code process involves two tasks - printing and reading - and the printer only affects one of them.)
3. Using unsuitable print media for the job.
4. Setting the printer darkness incorrectly.
5. Using the wrong print speed for the job.
6. Printing bar codes having insufficient bar width.
7. Printing bar codes using incorrect bar and space proportions.
8. Failing to encode start and stop characters or checksum characters correctly, for codes where these elements are not automatically calculated and printed.

You can avoid these errors with a little care. Follow these guidelines to produce reliable bar codes:

Always confirm that the chosen bar code symbology supports the characters you wish to encode. Keeping data on bar code symbology handy while writing label formats can help you avoid mistakes. The previous section covers the prominent features of most of the bar code symbologies supported by Cognitive printers.

Identify any bar code data that you must program manually. Sometimes you must include some hidden information, such as start and stop characters and checksum characters, along with the bar code data. The nature of such data depends on your printer and the chosen bar code symbology. Some printers automate many of these housekeeping chores, but nevertheless, you should be aware that:

• UPCA requires you to specify the number system type and enter it as part of the bar code data.
• I2OF5 uses a checksum, which you may have to calculate and enter as part of the bar code data.
• CODE39 sometimes requires a checksum. If your implementation of CODE39 requires a checksum, you may need to calculate it and enter it as part of the bar code data.
• CODABAR requires start and stop characters that you may need to enter as part of the bar code data.
• PLESSEY requires a checksum digit that you may need to enter as part of the bar code data.

(Of course, if you are using a label printing software package, the software should handle all of these issues more-or-less automatically. We don't mean to imply that store clerks need to know how to calculate checksums.)

Use a "systems approach" when setting up your bar code printer, scanner, and host computer. Resolve compatibility issues early. Since Cognitive printers support most bar code symbologies, developing a system that is compatible with your requirements should not be difficult.

Always use high-quality print media, and make sure that the media is suited to the application and its environment. Use thermal transfer printing when you expect labels to be in place for extended periods, or where labels may be exposed to intense heat or direct sunlight. Use vinyl labels and rub proof ribbon in harsh environments.

Do not print bar codes in color; many scanners can't see color. Avoid printing bar codes on media that has a colored background. The background color may reduce the bar and space contrast, possibly below your scanner's detection threshold.

Print bar codes as large as possible. Avoid printing bar codes that have less than a 10 mil minimum bar width. There are several ways to program the size of bar codes. Probably the easiest way to assure yourself that all bar codes are at least 10 mils wide is to always use a print pitch of 100 dots per inch or less, if your printer will support it (most Cognitive printers do).

300 DPI printers can safely print higher density codes. Bar widths as small as 5 mils should scan when printed on Barcode Blaster SR or similar printers. But as a general rule, large bar codes scan more reliably than small ones.

Adjust printer speed and darkness for optimum label printing. These settings tend to interact to a certain degree. Reducing print speed will often improve print quality.

Cognitive printers are factory set for optimum results with most popular media, but may need adjustment for different media or as the printer ages. Experiment with print darkness to find the best setting. Use a bar code verifier to check print darkness, if possible.

When considering print darkness, there is a difference between printing text and bar codes, especially rotated bar codes: Labels having text, boxes, graphics, and the like that "look good" are often too dark for reliable bar codes. This is because heat buildup on the printhead and print media makes the bars print wider than you expect. This changes the width ratio of the bars and spaces. When printing labels that have mixed text and bar codes, try reducing darkness if the text looks very dark, even if it looks sharp. Printing labels as light as possible also helps reduce printhead wear.

Special Considerations for Rotated Bar Codes

Note: Our Blaster Advantage and Solus printers use an advanced "dot history" algorithm to greatly reduce problems with rotated codes. If you are using an Advantage or a Solus printer you probably do not need to concern yourself much about the information in this section. (But if you are using another manufacturer's printer, then read on.)

There is one characteristic of thermal printing that sets it apart from other printing techniques: It takes time for a thermal printhead and print media to change temperature. Each dot on the printhead must get very hot to darken the thermal print media, and the dots take a little while to heat and cool as the drive voltage is applied and removed. The print media is in motion continuously, so while the dots are heating and cooling the print media is still exposed to some heat. Areas of the label that theoretically should stay white will be subjected to temperatures close to the darkening temperature. This results in some unavoidable bleeding of dark areas into light areas.

The severity of the bleeding depends on several factors, the most critical of which are:

• Print speed: As you increase the print speed, a larger area of the label will be exposed to heat during the cool-down period. This tends to increase bleeding.
• Media quality: Different media types have different heat sensitivity. Media also has a response time. Some media types are more subject to bleeding than others.
• Print temperature: The printer darkness setting controls print temperature. Up to a certain point, the higher the print temperature the darker the print will be. Excessive heat increases print bleeding.

Print bleeding affects rotated codes more than normal codes, because the bars of rotated codes travel perpendicular to the printhead as it heats and cools. With unrotated codes, the bars are traveling parallel to the printhead, so the width of the bars are subjected to heat for a shorter period of time. This is why unrotated codes generally look sharper and tend to scan more reliably than rotated codes.

Design labels using unrotated codes rather than rotated codes if you have a choice. If you must print rotated bar codes, there are several ways to improve scannability:

1. Always use high quality print media.
2. Print your labels at the slowest printer speed that is available and acceptable for the job requirements.
3. Experiment with print darkness to find the best darkness/speed combination for your printer and print media.
4. Print the bar codes as large as possible. Generally, the wider the bars the better the labels will scan.