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is a printer, each data line corresponds to one pin on the print head. Thus each byte sent will fire up to eight pins.
But the printer has 9 pins available. So how do you fire the ninth pin with only 8 data lines? In fact, do you really want to bother with just one extra pin? For this purpose, your printer has a special
0 | 128 |
|
L | ||
| 64 |
|
: | 32 |
|
E | 16 | ) First byte |
0 | 8 |
|
| 4 |
|
| 2 |
|
: | I | ! |
0 | 128 | Second byte |
|
(only the top bit is used)
Figure 7-8. The printer needs 2 bytes to tire all 9 pins in the 9-pin
graphics mode.
In addition, you can select the print density by the value qf n0. When nO is 0 the normal density is selected, and when nO is 1 the double density is selected.
Since computers are faster than printers, there is no signif- icant time loss in printing a single line of graphics with 9 pins. You get 9 dots per line in about the same time as you get 8 dots in the other graphics modes.