the same time, add up the numbers of the pins and send the sum to the printer. Therefore, with 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 figure below shows three examples of how to calculate the number that fires a particular pattern of pins.

128

FE 64

16

:8

22

7

4

134

With this numbering system, any combination of the eight pins adds up to a decimal number between 0 and 255, and no numbers are duplicated. Before you can put these numbers in a graphics program, however, you need to know the format for graphics commands.

Graphics commands

Graphics commands are quite different from most other commands. For most of the other modes, such as emphasized and double-wide, one command turns the mode on and another turns it off. For graphics, the command is more complicated because the command that turns on a graphics mode also specifies how many columns of graphics will be printed. After the printer receives this command, it interprets the next numbers as pin patterns and prints them on the paper.

The graphics command format

There are several different graphics commands giving different horizontal dot densities and printing speeds. Because the format is almost the same for all the commands, however, the example here keeps things simple by using only the single-density graphics command, ESC K. In single- density graphics, there are 60 dots per inch horizontally.

Using Software and Graphics

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