Epson LQ-2550 User Manual - Page 120

Twenty-four-pin graphics The graphics mode that takes full advantage of the printer's print head is 24-pin graphics. This mode has five densities, but for simplicity this explanation begins with triple-density. Triple-density prints up to 180 dots per inch horizontally. As the print head moves across the paper, it must receive instructions every l/180th of an inch about which of its 24 pins to fire. At each position it can fire any number of pins from none to 24. This means that the printer must receive 24 bits of information for each column it prints. Since the printer uses B-bit bytes of information in its communication with the computer, it needs three bytes of information for each position. Pin labels To tell the printer which pins to fire in each column, you first divide each of the vertical columns into three sections of eight pins each and consider each section separately. Since there are 256 possible combinations of the eight pins in each section, you need a numbering system that allows you to use a single number to specify which of the 256 possible patterns you want. This numbering system is shown below: 128 iii 16 : 2 1 To fire any one pin, you send its number. To fire more than one pin at the same time, you add up the numbers of the pins and send the sum to the printer. Using these labels for the pins, you fire the top pin by sending 128. To fire the bottom pin, you send 1. If you want to fire only the top and bottom pins, you simply add 128 and 1, and send 129. By adding the appropriate label numbers together, you can fire any combination of pins. The following three examples show you how to calculate the number that will fire a particular pattern of pins. Using Software and Graphics 4-15