Dot Matrix Printer Overview – Types of Dot Matrix Printers and Its Printing Process

Dot Matrix Printer (or Impact Matrix Printer) is one of the first models of computer printer that involves print head running in back and forth motion or horizontally across the page and prints mainly by impact of pins striking the paper through an ink ribbon cable forming bunch of dots for printing each letter.

Different types of Dot Matrix Printers

1. Based on printing directions, Dot matrix printers are classified into two types namely, unidirectional and bidirectional printers. A unidirectional printer prints only in one direction i.e., from left to right whereas, a bi-directional printer prints in both the directions – from left to right & right to left.
2. According to number of pins or dots used per letter, there are mainly 3 types of printers – 9 pin, 18 pin and 24 pin.
3. Based on the movement of print head, there is 80 column printers and 132 column printers. In these two types of printers, the print head moves 80 columns and 132 columns respectively.
4. According to print color, there is monochrome printer and color printer. Monochrome printer prints only one color (black) and color dot matrix printer is made to print a maximum of 4 colors – Red, Green, Blue and Black.

Printing Process in Dot Matrix Printer:

1. First the computer sends a series of ASCII codes to the printer.
2. The ASCII codes received by the printer are first stored in the RAM buffer.
3. The bitmap table contained in the printer’s ROM chip tells the printer the pattern of dots it should use to produce the required character shape represented by the ASCII code.
4. The printer processor takes the dot pattern information from bitmap table and send the signals to the printer head.
5. The printer head contains 9, 18 or 24 pins aligned vertically such that one end of each pin is connected to individual electromagnet.
6. To fire the print pins against the ribbon and paper this electromagnet is energized due to which the moving pin strikes the ribbon that is coated with ink.
7. After the pin fires, the electromagnet is de-energized which makes the spring pull the print pin back.

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