Help for Beginners
|What is a barcode?
|Why use them?
|Where are they used?
|The Different Technologies
"barcode" is a method of automatic identification which allows information to be captured quickly and accurately by a computer. A barcode symbol consists of a series of bars and spaces of various thickness. These are broken down into groups of bar / space patterns which represent individual human recognisable characters.
Example barcode Construction (Human Readable):
Notice each barcode character consists of five black bars and four inter-spaced white spaces - 9 "elements" in all. Of the elements, one white space and two black bars are double thickness - three thick elements in total. Hence the original name of the barcode - Code 3 of 9, now more usually shortened to Code 39. Combining the above, we get the more usual appearance:
For different applications, different sets of rules are used to convert characters into bar / space patterns. Each set of rules is called a different "Symbology". For example in the European retail industry, the EAN (European Article Numbering) symbology is used for goods scanned at the point of sale.
The information contained in a printed barcode is converted back into recognisable form by a barcode scanner and decoder. The scanner converts an optical image of the barcode into an electronic signal. This is fed to the decoder which reproduces the original information. This process can take a fraction of a second.
With modern barcode readers, to save cost and space, the decoder tends to be incorporated into the scanner unit.
Those retailers who have invested heavily in Information Technology (IT) have proved time and time again that despite considerable initial investment they have made massive savings in costs as a result. Typical figures quoted suggest a 2% (of costs) investment in IT technology leads to an overall 6% saving. That makes an enormous difference to profits. Similar benefits can apply to practically any business.
In essence, IT provides management with very detailed up to date information on key aspects of the business and allows decisions to be made quicker and with more confidence. Taking retail as an example, fast selling items can be identified quickly and automatically re-ordered to meet demand. Slow selling items can be identified preventing a build up of unwanted stock.
More sophisticated systems will use historical data to predict seasonal fluctuations very accurately. Seasonal goods are therefore ordered exactly when required and in sufficient quantity to match demand. The effects of re-positioning a given product within a store can be monitored allowing fast moving more profitable items to occupy the best space.
Many more benefits are available from such systems, but they are only as good as the quality of the data that is fed in. Speed and accuracy of data entry is a vital consideration. At the point of sale, for example, it would be impossible for the checkout assistant to type in details of every product sold to every customer, the queues would be unbearable and the captured data inaccurate. Studies have shown that on average one error occurs every 300 key presses during manual data entry.
The solution is barcodes. A checkout operator might take three seconds to key in a 13 digit product code. A barcode scanner can do the same in a fraction of a second. One product description in twenty three could be wrong with manual entry. Perhaps one in a hundred thousand would be wrong using barcodes.
Other methods of automatic data entry are available such as optical character recognition (OCR) but no other method offers the benefits of low cost, flexible label production and relatively low cost scanning equipment.
barcodes can and should be used anywhere where an IT system requires fast and / or accurate data entry. The most common application is in shops and supermarkets where all items are barcoded. Here are some more examples:
Many sophisticated "automatic warehouses" are now in use. barcoded containers of raw materials are stored in racks of bins, which are also barcoded. When goods are put into the warehouse, the computer system instructs an automatic crane to retrieve the nearest available empty bin. The filled bin is then returned to an empty location. The crane relies entirely on barcodes to locate and move goods in and out. The computer system can usually position goods which are regularly used closest to the front of the racks to minimise access times and improve efficiency. There is no human access to the racks, so stock control data is much more accurate.
Transport and distribution
All major road freight carriers now use barcodes. Individual packages are barcoded as are depot consignments. The exact location of any package is known at any one time together with details of the type of service used. Individual customers can be billed quickly and efficiently and missing parcels can be traced more easily.
Very accurate data relating to work in progress (WIP) can be obtained using barcodes as the data entry method. Management can obtain up to date data on the progress of unfinished product, enabling bottle necks and over production to be reduced and production efficiency to improve.
Spares and Maintenance
Many computer maintenance companies now barcode all goods returned for repair. The exact location of any unit, repair progress to date and estimated completion date can be obtained easily. Through more efficient resource control, goods can be repaired quicker and more cheaply. The automotive industry has adopted barcodes to identify spares and improve distribution.
Many polling companies now use barcoded multiple choice questionnaires to enter data quickly and accurately. Survey times can be dramatically reduced.
barcodes are commonly used to identify blood and other samples. Accuracy of data is essential and barcode entry is far superior to manual. Hospital patients and out patients records are increasingly barcoded for fast retrieval and better integrity.
Many library systems have been enhanced using barcodes to record loan transactions and provide more detailed information on stock.
Many large retailers now insist that their suppliers not only barcode individually packaged items, but also cartons of bulk packed items. This is part of an electronic trading system called EDI (Electronic Data Interchange). This defines a standard protocol which links the supplier's and customer's IT systems. Goods can be re-ordered or returned automatically. Received goods are recorded as they leave the truck by barcode scanning. Both supplier and receiver IT systems can be updated. This efficient system offers benefits to both supplier and customer.
Banking, insurance and local government
barcodes are now used extensively for accurate document control and retrieval.
Time and Attendance
There are many applications where you might need to record the presence or activity of people. For example a clocking system for shift workers, recording delegate movements at an exhibition or conference, hospital consultants or solicitors recording time spent on each activity. Give each person a barcoded badge and you can monitor their movements using any computer system which has a real time clock.
There are many different types of barcode, referred to as symbologies. Each symbology is designed to optimise one or more important parameters such as:
- High information density, or high resolution. Very small codes can be printed and used on items where space is limited, eg printed circuit boards.
- Optimum data integrity, where the possibility of read errors is practically zero. This is most important in health care.
- Easy to decode. Some codes use simple coding techniques and are widely supported by scanner manufacturers.
- Codes such as those used in retail have a well defined data content. They are structured to ensure conformity across a wide number of users.
- Some codes are designed to offer a very wide character set while others will support numeric data only.
EAN means European Article Numbering, a European wide system for uniquely defining goods which are sold in shops and supermarkets. Each product is allocated a unique 13 digit number, or 8 digit number for smaller goods such as cigarette packets. Their use in the UK is controlled by the Article Number Association (ANA).
The first 7 digits of the 13 digit code are allocated by the ANA to its members, generally consumer goods manufacturers or suppliers. With some exceptions such as publications, own brand goods and variable weight goods, products produced in the UK start with "50". The following 5 digits are the manufacturer's unique ID number. The manufacturer allocates its own unique product identification number to the next 5 digits. The 13th digit is an error check character to help the scanner to prevent misreads. Supplementary codes, "Add on 2" and "Add on 5" can be used to provide additional information:
Add on 2 is used with periodicals to denote the week or month of issue.
Add on 5 is often used with books to code the retail price. A shortened version of EAN-13 is available to barcode small items where only limited print space is available on the packaging.
This is called EAN-8, and provides 7 digit unique numbers, plus the error check digit. UPC-A and UPC-E have a similar structure to EAN but relate to goods produced in the USA.
Please note: There are many variables and regulations which affect the structure of EAN codes, especially where weighed goods and other limited circulation numbers are concerned. If you plan to print barcodes for use in retail applications, you are strongly advised to obtain full information from the ANA. Please see Further Information for their details.
This is a high density, variable length, numeric only code. It is common in transport and distribution where very large numbers are required to uniquely identify packages. In the UK it is also used extensively in shoe retailing.
The code begins and ends with a special start character and stop character. Within the data, odd characters (ie first, third, fifth etc) are encoded in a sequence of five bars, two thick, three thin. Even characters (ie second, fourth etc) are encoded in the sequence of five white spaces which interleave the previous odd character.
The simple nature of the code means it is one of the least secure. Scanners may return only part of the encoded data. Use of a check digit, bearer bars, and scanning equipment programmed to look for a fixed length of code will dramatically improve security.
A special version of ITF, called ITF14, is used on outer case cartons of bulk retail goods. The content of the code is usually the same as that of the EAN barcode on the enclosed goods, with one additional character.
The code is enclosed in a thick black lines, called bearer bars. These help prevent scanners from scanning only part of the barcode.
This is one of the most secure codes and is often used with blood samples and similar. It is variable length.
The character set consists of numbers 0 to 9 plus six special characters : / . + - $. A choice of four start / stop characters A B C D is also available allowing the user to categorise information. Each character is represented by four bars and their three integral spaces.
One of the first barcodes to be developed, it is the most commonly used outside of retail. 44 characters may be encoded including numbers and all capital letters.
Each character consists of five bars (two of which are thick) and the enclosed four spaces (one of which is thick). Each character therefore consists of 9 bars (five black, four white), three of which are thick, hence the original name "Code 3 of 9".
It is an excellent general purpose code which is easy to decode, but not very compact. Code 39 data always begins and ends with the asterisk character.
This is a high density alphanumeric symbology which uses the full 128 ascii character set. It is sub-divided into three character sets, A, B and C. Used in its numeric only form (Set C) it is extremely compact.
Code 128 is an extremely versatile symbology. It has been adopted by the ANA in a special format ("EAN 128") for use with the distribution of traded retail goods. A special Fn1 character starts off the barcode data to denote this type of code.
Please note: There are many variables and regulations which affect the structure of the EAN128 barcodes. If you plan to print EAN 128 codes for use in retail you are strongly advised to obtain full information from the ANA.
Many 2D barcode symbologies have been introduced in recent years, primarily to pack more barcoded data into the same available space available for a one dimensional barcode. For example, the leading 2D symbology, called PDF417, could cram 2000 characters into the same space occupied by a one dimensional barcode containing 20 characters.
2D codes are used widely for carton identification in the freight industry and are appearing more on identity cards. However the applications are specialised and the scanning equipment is relatively expensive. For the vast majority of applications, one dimensional codes will meet the requirements.
A popular misconception It is important to understand how one-dimensional barcodes are used, and the nature of the information they contain. Take a retail barcode, EAN13. It is simply a reference number, a key to obtain information stored elsewhere in a computer system. The barcode itself does not usually contain a description of the goods, or a price, (although a special format is available for variable weight goods such as meat or fish). The barcode number is used to look up that information in a data base stored in the host computer. Whatever the application, one-dimensional barcodes are generally used in this way.
Who does the printing?
There are many different ways to print barcodes, you need to select the best option for your application. The first choice is whether to print your labels or forms using an external print bureau, or to print "in house".
Print bureaux are attractive for very large print runs, 50,000 labels upwards, or for specials - for example labels which are very small, tolerant to high temperatures, or extremely durable. At high volume, cost per printed label will be little different to the cost of purchasing blank label stock for an in house printer. Print bureaux are not suitable for on demand labelling and are generally not cost effective for small print runs.
Printing "in house" incurs a start up cost to purchase barcode fonts or labelling software and printer hardware. However you have total control over the layout and content of the labels. You can merge variable data from your existing computer system and you can produce very small print runs, even individual labels, on demand.
How barcodes are printed in house?
Just like text, barcodes are available in fonts. For PCs, True Type barcode fonts are available for the Windows environment. They are installed in the same way as any other Windows font.
They can be used in any Windows application and will print to any printer installed with a Windows driver. barcodes can be incorporated into any document using this method. One point of caution, however - EAN, UPC, Interleaved 2 of 5 and Code 128 fonts are not as straight forward as they first seem. Check digits are used, or characters are encoded in pairs, or special format characters are required. For these, calculation utilities are used. You key in the information to be bar-coded. The utility re-formats the text to include the additional information. The new text must be copied and pasted into the application program. If you are using a package which supports Dynamic Link Libraries (DLLs), then a font package such as barcode Pro (detailed in the catalogue) can be used to automate this process.
Similar fonts are available for DOS applications, supplied in the form of Terminate and Stay Ready (TSR) memory resident programs. These are more difficult to use as the barcode data will only appear on the PC screen as text when the document is created or edited. The specially tagged text is converted to barcode by the TSR as the data is sent to the printer.
For PCs printing to an office printer, DOS and Windows labelling programs are available. They contain their own barcode fonts, but these may not be accessed by other programs. For UNIX systems, use a module containing barcode fonts which connects in line with the printer's parallel port. Specially tagged text is converted to barcode as data is sent to the printer.
One note of caution - care must be taken when printing barcodes to dot matrix or ink jet office printers, where print quality can seriously affect the readability of the barcode. Always check that the labels can be easily read by the scanner which will be used in the final application.
Specialized printers are available for in house label production. These are either "Direct Thermal" or "Thermal Transfer". Both use a print head containing an array of tiny heating elements. They often have built in barcode fonts, particularly important if you have a terminal based system running UNIX for example where label design and print software is relatively expensive. Instead the printer can be driven by a few simple ASCII text commands. A direct thermal printer requires special paper which is impregnated with a clear chemical film.
When the paper is heated by a print head element, a chemical reaction occurs which turns the film black. Characters are formed by selectively heating elements on the print head array which covers the full width of the label stationery.
Even after the thermal label paper has passed through a direct thermal printer, it remains sensitive to heat and ultra violet light. Serious label degradation can occur over time if the labels are exposed to these elements. Direct thermal printers do not, however, require any consumables such as toner or ribbons. They are ideal for receipt printing, and for labels where there will be no appreciable shelf life.
In a thermal transfer printer the print head elements generate sufficient heat to release a pigment from an impregnated ribbon which is then pressed onto the label.
A choice of ribbon types is available. Wax ribbons are the least expensive and apply easily. They can be smudged relatively easily, however. Resin ribbons are the most durable (smudge free), but are more expensive and difficult to apply. Wax - resin ribbons are a good compromise.
Thermal transfer printers are slightly more expensive than direct thermal and require regular renewal of the print ribbon. Typically one roll of print ribbon will last for two rolls of paper. They can, however, print on any type of paper or other materials such as polyester and the labels do not degrade over time from Ultra Violet exposure or heat. Both direct thermal and thermal transfer printers produce labels at about the same speed and cost. In general this is considerably faster than labels produced by office impact or laser jet printers.
Where to get blank labels and ribbons
For standard dot matrix, laser jet or ink jet office printers, manufacturers such as Avery provide a wide range of label stock. Whilst we do not include Avery labels in this catalogue, we supply to order. Please call with your requirements.
We stock commonly used sizes of paper labels for our Thermal / Thermal Transfer printers, but also have partnerships with specialist label and ribbon suppliers who offer labels to suit most applications. If you don't see what you need in the catalogue, please call us - we will probably be able to supply what you want quickly, saving you time and money. You can choose from different label adhesives, from easy peel through to tamper evident. Thermal transfer printers will print on practically anything, so a wide range of media is available, not just paper.
Print quality and verification.
barcode data capture systems can be rendered completely useless if care is not taken to ensure adequate print quality. barcode scanners require labels of reasonable quality to operate at maximum performance. Often the scanner is blamed, when in fact the problem lies with poorly printed labels.
Labels may not be of sufficient quality for many reasons. Here are some common examples.
- The print ribbon may be old and the printed labels too feint.
- The colour combination of bars to the label background may be unacceptable.
- The label program may not print in strict accordance with the symbology specification.
- The reflectivity of the paper may be insufficient.
- The printing may be too feint - the contrast between the dark bars and light spaces may be insufficient.
- There may be specks and voids in the barcode as a result of the print process.
- You may be trying to print the barcodes too small - at a higher resolution than the print process is capable of.
If possible, it is prudent to "test read" newly printed barcodes with the scanner which will be used in the actual application. If this is not possible then an investment in a barcode verifier is recommended. barcode verifiers undertake a range of checks on print quality. They produce a report which details the key parameters affecting the readability of the sample. Portable verifiers are available for applications where it is not possible to get the barcodes close to a computer. Some printers also have built in verifiers. These are particularly recommended for large print runs, or runs where barcode quality must be at an optimum. Ask for details of the Eltron Qualabar printers. Here, every single label is scanned after printing. Throughout the print run, the printer tests the print quality and automatically adjusts its settings to maintain optimum contrast. Any labels which are not top quality are automatically re-printed.
Things to consider when buying a thermal printer:
Most thermal transfer printers are 200 dots per inch (dpi). That's 8 dots per mm. Whilst barcodes will print perfectly at this resolution, text and graphics may appear slightly jagged. 300 dpi printers are more expensive, but worth the extra if fine print is a must.
Thermal print heads come in standard sizes - typically 2, 4, 6 and 8 inches. Decide what your label size needs to be and pick a printer capable of supporting that width. All manufacturers should state a minimum label width you can use for a printer, typically 1 inch (25mm). You could therefore use a 4 inch printer to print 1 inch wide labels, and keep some flexibility for new label sizes in the future. Label stock can be narrow edge leading (portrait), or wide edge leading (landscape). One point of particular note - barcodes will print perfectly if in "picket fence" orientation, where the bars point in the same direction of travel as the paper. Because of printer motor tolerances, the results may not be as good if the barcodes are rotated 90 degrees and printed in "ladder" format. The resulting variations in bar / space widths may cause scanning problems. Therefore, try to choose your printer and label design such that ladder format is avoided.
As a general rule, print speed increases with cost. 2 inch (50mm) per second is typical for a low cost thermal printer, and adequate for low volume printing. 6 or 10 inch (254 mm) per second printers are available is speed is a key requirement.
This is basically how many labels you will get on a roll, and is usually specified in terms of the maximum outer diameter (OD) of paper roll which will fit the printer. The smaller the OD, the more often you will need to replenish the labels. For low volume printing this is rarely a consideration.
Make sure your choice of printer can support and additional features you may require, and when making price comparisons, make sure you compare like with like. Some suppliers double their prices after adding the extras. Options to consider include:
This may be required to print large labels - ask us for advice.
Keyboard Display Unit
allows a printer to be used independently of a host computer.
for automatic cutting of continuous label stock.
for batch label production.
This software allows the printer to be installed in Windows. Therefore you can print to it from any Windows application program.
We offer a number of different types of barcode reader, each particularly suited for certain applications. Use the following information as a guide to help you to pick out the type most appropriate for your needs.
In general, barcode readers contain a light source, photo detector and signal processing circuitry. The light source shines light onto the barcode which is then reflected back into the scanner and focused onto the photo detector. This converts the optical information into an electrical signal which is "cleaned up" with further circuitry and converted to a signal format which will be recognised by the device to which the barcode reader is connected. The light source is at a wavelength and intensity which is designed to optimise the performance of the photo detector.
Some scanners have built in decoders to convert the barcoded information into a standard format (such as ASCII) which is recognised by a computer. Other scanners rely on the host computer to do the decoding.
Whatever type of host equipment is used, the scanner usually requires an external source of power. For portable applications, this can be the major factor when selecting the type of scanner you require.
A wide range of barcode scanners are available. Price and performance vary considerably. Here are the most popular types.
These have the advantages of low cost and low current consumption. They are most often used with hand held terminals. Reading is achieved by placing the scanner at one end of the code at a slight angle and moving it briskly across the code at a constant speed. Pens use one or more LEDs as a light source. These may emit visible or infra red light. The latter are used in security applications where the barcode is obscured by a black film which is invisible to the scanner. As the tip of the pen is in contact with the barcode, tip wear and code wear problems can be experienced. With poor quality codes, the pen may need to be swiped several times to obtain a "good read." For optimum use, operator training is required. Codes on loose packaged items such as crisps are difficult to read with this type of scanner.
These use CCD type photo detectors similar to those used in electronic cameras and allow a complete image across the barcode to be scanned continuously. This removes the need to physically swipe the scanner across the code. The whole barcode is illuminated by a row of LEDs and the CCD sensor will "take a picture" of the code typically 100 times per second. In general, CCD scanners must be positioned within 1 or 2 cm of the code, but unlike pen scanners, code wear is avoided. They are most commonly used in retail applications where the type and size of code is well defined. In general, codes which are larger than the width of the line of LEDs cannot be read, so care must be taken to select the correct size of scanner. Long Range CCD scanners are available with a greater depth of field typically 10cm. However, since they are more expensive, consider low cost hand held laser scanners as a better general option. Make sure you look out for low power CCD scanners when you are connecting to portable computers. With no moving parts, these types of scanner are extremely reliable and offer rapid read rates. They are an ideal entry level investment.
Hand Held Laser Scanners
Of the three hand held technologies available, laser scanning is the most flexible, but also the most expensive. Scanners are often gun shaped, firing a scanning laser beam when the trigger is squeezed. Usually a laser diode is used as the light source. The beam is reflected off the barcode and back into the gun through a large lens to a photo detector. A moving mirror arrangement is used to scan the beam at a constant speed. This process is repeated typically 33 times per second. With this method, codes can be scanned from a distance and the size of the code is not critical as with CCD scanners. Both visible and infra red laser diodes are used, visible being the most popular for general applications. A typical maximum reading distances for a laser scanner are 30 - 90 cm although long range versions are available which can read in excess of 10 metres. However, the greater the distance, the larger the code must be, and the better the print contrast. For very long range scanning, special reflective media must be used. As laser scanner range increases, so does cost. In practice, scanning range is normally limited by the size (or resolution) of the barcode. Imagine an eye test. The smaller the printing, the closer you must be to read character. Irrespective of the maximum range of the scanner, it will only be able to read a small code at close range. As a general guide, a standard size EAN13 barcode can be read by any laser scanner to a maximum distance of about 30cm. Technical literature will show a "field pattern" diagram to relate the size of barcode to the operating range of the laser: Lasers are often used in portable applications where codes are not easily accessible, or in fixed positions such as DIY shop checkouts where the goods are too bulky to be positioned close to the scanner. Particularly suitable here are cordless laser scanners, using short range RF to replace the cable.
Fixed Position Scanners
There are many types of fixed position scanner, using pen, CCD and Laser technology. The most popular is the omnidirectional laser scanner, also called "Flatbed" or "Projection Scanner". Commonly used in large supermarkets, they use an array of mirrors to produce three dimensional patterns of scan lines. When a barcode passes over the pattern in whatever orientation, usually one scan line will cross through the full width of the code allowing a good read. These scanners are relatively expensive, but ideal for applications where a high throughput of codes is expected and where both operator's hands should be free to move coded goods. Look out for omnidirectional hand scanners, compact flatbed scanners which can be used "hands free", yet are small enough to be picked up to reach over a counter to scan bulky items. Whilst their performance is not quite as good as conventional flatbed scanners, they are less expensive and more flexible. Commercial holographic laser scanners are now in production, giving high performance omni-directional scanning over a wide area. These are particularly suitable for container tracking in freight distribution centres. Another type of fixed position scanner is the "slot reader". The technology used is similar to pen scanners, except in this case the scanner is fixed and the barcode is swiped through a slot in much the same way as a credit card would be on a till. Slot readers are common in time & attendance and access control systems. They operate in a similar way to credit card readers - a barcoded card is swiped through a slot to obtain a good read. Other fixed scanners are specifically designed for industrial conveyor systems and automated production equipment. They are metal cased and have inputs for external triggering from devices such as photo-sensors. They often have digital outputs or relays, which can be activated if the unit is triggered but no barcode is read. In a typical application with barcode labelled boxes travelling along a conveyor, the barcode scanner would cause the conveyor to stop if a box had an unreadable or missing barcode label. Modern industrial scanners can be programmed from a PC to produce different types of scan pattern to optimise scanning for a particular application.
Interfacing to a host computer
Several methods are available to connect barcode scanners to a host computer. We have a large data base detailing the interfaces available for most PCs, terminals, EPoS units, portable terminals etc. We fit the correct connectors and pre-program scanners before we ship to you.
Most computing devices have an RS232 interface, some are specifically modified for scanning. A standard RS232 interface will not provide a 5v supply typically required to power a hand scanner, so an external power supply will be required.
Used in systems where dumb terminals communicate to a mini or mainframe computer via RS232. The scanner connects between the terminal and mainframe and therefore has two RS232 interfaces. Usually a scanner with this type of interface requires a mains adapter to provide power. RS232 data from the scanner is multiplexed onto terminal TX line to the host and therefore appears to the application software as keystrokes. This method will not work if terminals are run in ANSI mode.
Many hand held terminals have an interface specifically designed for a barcode pen. Many CCD and laser scanners are available with an output which appears identical to that which would be provided by a non decoding pen.
"Optically Coupled Interface Adapter". This is a synchronous interface in many other respects similar to RS232. It is used extensively on EPoS equipment. We offer CCD, laser and flatbed products supporting this interface.
The vast majority of PCs and computer terminals do not incorporate a dedicated barcode reader interface. Similarly most application software is written only for keyboard entry of data such as part numbers, product codes etc. A Wedge interface sends data to the host in the form of emulated keystrokes. In this way, the application software sees no difference between data which is keyed in, and data which is read in, by a barcode reader. "Keyboard Wedge" interfaces are commonly used with PCs. They are connected between the keyboard and the system unit drawing power from the existing keyboard supply. Unsightly additional power supplies are thus avoided. They may be in the form of a "black box" to which a barcode scanner is attached, or more usually they will be integrated within the scanner housing.
Software Wedge programs are available for PCs. They take barcode data from an RS232 port and place it in the keyboard buffer as if it were typed. These programs are available for Windows or DOS based applications. During normal operation, they will not be visible to the user and do not require any alterations to your application software.
A Terminal Wedge interface (sometimes called "eavesdrop" wedge) is available for dumb terminals in addition to keyboard wedge. This is the same as the Dual RS232 interface described above.