9-Pin Graphics Mode - Epson FX-80 User Manual

9-Pin Graphics Mode
Recall that in the last chapter we said that the bottom (ninth) pin of
the print head is not normally used in the Graphics Modes. That's
because most microcomputers communicate with parallel type pe-
ripheral devices using eight data lines (even if they have 16-bit proces-
sors). With 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 nine pins available. So how do we fire the ninth
pin with only eight data lines? In fact, do we really want to bother
with just one extra pin? Well, for such graphics-intensive applications
as screen dumps, printing nine pins at a time can speed up the process
considerably. For this purpose, the FX-80 has a special 9-Pin Graphics
Mode (but not for 7-bit computers). In this mode the printer takes two
bytes to fire all nine pins-as shown in Figure 13-5.
128
64
32
16
8
4
2
1
128
64
32
16
8 '---_ _
---I
4
2
1
First 8 bits
Second 8 bits
Figure 13·5. g·pin graphics.
149