Let me take this opportunity to wish everyone a Happy, Healthy and Prosperous New Year for 2012! Now let's continue on with our selection of a kiosk printer. Read Parts 1-4 here.

We're now up to the interface type. There are numerous interfaces that can be used to connect the printer to your host system. Most printer models are available in several different interface types; some may contain more than one interface type in a single unit. The first issue that influences your choice of interface is to decide whether the printer will use text or graphic printing. This requires some explanation.

There are normally two ways to print from a thermal printer. You can use the printer's own internal character generator to create the characters to be printed, or you can send the characters as graphics. There are advantages and disadvantages to each, but it's important to decide which you will use, because this is a key consideration in choosing the interface type.

Text Printing: In text printing, an ASCII code that represents a character is sent to the printer, along with positioning commands, where needed. The printer accepts this code, looks up what character it represents in its internal storage, and prints it on the paper.

Advantages

• Fewer bytes must be sent per character.
• Faster data transfer due to fewer bytes being sent.
• A slow interface type may be used since not very much data is being sent.

Disadvantages

• Printed output is limited to the fonts stored in the printer.
• It is awkward to mix graphics with the text.
• What is displayed on the screen is NOT exactly what you get.
• Different printers require different commands from your host program to perform the same function.

Graphic Printing: In graphic printing, which is most often used with Windows or other operating systems, what you see on the screen is transmitted as graphics to the printer. Everything is sent as graphics by specifying each individual pixel, including text. If you print to an ink jet or laser printer from your home PC, you are almost certainly using graphic printing.

Advantages

• Can easily print anything, including images.
• What you see on screen IS what you get.
• If you can make the font on the screen, you can print it.
• Printer manufacturer supplies a driver to allow easy integration with operating system.

Disadvantages

• Many more bytes needed to print that text printing
• Requires a high speed interface

What's all this mean to us? Basically, if you use text printing, you can use an RS-232 interface because you're not sending much data, and RS-232 is relatively slow. But if you use a Windows or Linux driver, you are printing graphics, and need to use USB or another high-speed interface to achieve reasonable print speeds, especially if the printout is wider and more information must be sent to represent a single printed line.

The most common interfaces that you will notice in modern printers are USB, RS-232, and Ethernet. There are a variety of others that are not yet broadly popular or are used in very limited applications (Bluetooth, for example). There are also a few older interfaces that are sometimes considered (Centronics parallel, for example).

A few highlights of each type are:

USB: Ubiquitous in computers for everything from the mouse, keyboard, scanner and printer, USB interfaces are available in several different versions: 1.1, 2.0 and, most recently, 3.0. The higher the number, the faster the communication speed. However, from the printer's perspective, USB 1.1 sends data faster than the printer can print for most applications (A4/letter width printers can take advantage of the faster USB 2.0) and is generally adequate. These are cross-compatible, so that a host running USB 2.0 can use a USB 1.1 printer. Generally speaking, USB is faster than the other commonly available interfaces. I always recommend it whenever possible. If you are not using a print driver, it's a bit more difficult to set up, but the added speed is worth it.

RS-232: This is a very simple interface that is often found in legacy systems and less sophisticated host equipment. Its primary advantage is its simplicity, while its primary disadvantage is its slow speed. Even at fast baud rates of 115,200 baud, it is noticeably slower than USB 1.1.

Ethernet: A printer employing an Ethernet interface can be plugged directly into your computer network without the need for additional wiring. This makes it especially convenient for certain types of applications where multiple printers are required, such as POS systems. In some printers with an Ethernet interface, the Ethernet connection is only used for information concerning the printer's status, not to send data to the printer itself.

In general, I would suggest using USB whenever possible, with RS-232 as a usable choice for narrower receipt width printers, especially when using text printing. Ethernet should be used where the printer may often need to be relocated, such as department store POS systems, or where the printer is located a very long distance from the host.

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