Graphics data

After receiving a graphics command such as ESC K nl n2, the printer prints the number of codes specified by nl and n2 as graphics data, no matter what codes they are. This means that you must be sure to supply exactly the right amount of graphics data. If you supply too little, the printer will stop and wait for more data and will seem to be locked. The next data sent will then be printed as graphics, even if it is really text. On the other hand, if you supply too much graphics data, the excess will be printed as regular text.

Simple Graphics Programming

The first example in this section shows how a graphics command, column reservation numbers, and data can be used to print a single line of graphics. The example is a BASIC program. If you prefer another programming language, the principles are exactly the same. Therefore, you can easily adapt the program to the language you prefer.

The first line of the program specifies single-density graphics for 40 columns:

100 LPRINT CHR$(27);"K";CHR$(40);CHR$(0);

The second line is the data that is printed as pin patterns. It uses the number 74 to produce one of the patterns shown in Figure 6-1. The FOR-NEXT loop sends 40 columns of data.

200 FOR X=1 TO 40: LPRINT CHR$(74);: NEXT X

That is the whole program. In BASIC, semicolons at the ends of the lines are very important; they prevent the computer from sending other codes after the ones you specify. In other languages you may have to use a special command to send a single code at a time. Run the program to see the result below. Although it is not as interesting as the examples at the beginning of this chapter, it shows exactly how the mode works.

6.6

Introduction to Dot Graphics