Star Micronics NP-IO manual Printer needs 2 bytes to fire all 9 pins in the g-pin

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peripheral devices using eight data lines. When the peripheral 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? Well, for such graphics-intensive applications as screen dumps, printing 9 pins at a time can speed up the process considerably. For this purpose, your printer has a special g-pin graphics mode (it won’t, however, work with 7-bit interface systems). In this mode the printer takes 2 bytes to fire all 9 pins as shown in Figure 6-8.

0	128
	64
:	32
	16	First byte
:
	8
0	4
0	2
	1 J
E	128	Second byte

Ij

(Only the top bit is used)

Figure 6-8.The printer needs 2 bytes to fire all 9 pins in the g-pin

graphics mode.

In addition, you can select the print density by the value of no. When n0 is 0 the normal density is selcted, and when n0 is 1 the double density is selected.

Since computers are faster than printers, there is no signifi- cant 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.