Thread: Dot Matrix Printing Operation

Compared to tho'se of inkjet and laser printers (discussed later in this chapter), the operations of the dot matrix printer are fairly simple. However, printing data on a dot matrix printer does involve quite a few steps, many of which are also used with all other printer types.

The printing process for any type of printer always begins with the PC and its software. Typically, an application program, such as a word processor (e.g., Microsoft Word, Corel WordPerfect), a graphics package (e.g., Adobe Illustrator, Photoshop),or a . desktop publishing package (e.g., Microsoft Publisher, Adobe PageMaker), generates a print-image file, which can be anything from a plain text document to a complex full-color photograph. The following on a dot matrix printer.



After a user sends a document to the printer, the application in use communicates to the PC's operating system and the printer's device drivers to create a file that contains print commands and codes used by the printer to create the document. The commands included in this file are those needed to produce the letters, numbers, special characters, graphics, print styles, and other document effects, such as tabs, line feeds, and page feeds. This file is placed in the system's print queue, which is a buffer that holds print files waiting to be sent to a printer. When the printer is available, the file is sent to the printer. Otherwise, the print file is held until the printer is available and there are no other print files in the queue ahead of it.

When a print file is transferred to a dot matrix printer, it is stored in the printer's print buffer. The print buffer is needed because the PC transfers data to the printer much faster than the printer is able to print it. The print buffer receives the print file and releases the PC to perform other tasks. Without a print buffer, the PC would have to wait while the printer processed each line of the print file and printed the data. Early PC printers either had no print buffer or had a very small one. This meant that the PC and the printer were both tied up until the printing job would complete.
Dot matrix print buffers typically hold 8 to 60 kilobytes (KB) of data, depending on the manufacturer, and model of the printer. Dot matrix printers with enhanced graphics or extended font capabilities tend to have larger print buffers. The size of a dot matrix printer's print buffer is commonly listed right along with its print speed as one of its major features and more is always better.

Often the size of the print file exceeds the capacity of the print buffer. When the print buffer is full, it sends a command to the PC to stop sending data. Typically, this is a transmission off (XOFF) command. As the printer empties the print buffer and more space is available, the printer notifies the PC with a transmission on (XON) command that it can resume sending the file. This dialogue continues until the entire file is transferred.' After the file is completely transferred to the printer, the computer disengages and moves on to other tasks while the printer finishes printing the file. These communications are not specific just to dot matrix printers.