Chapter 7: Graphics Commands For 24-Pin Printers; Overview - Oki MICROLINE ML521 Reference Manual

Chapter 7: Graphics Commands for 24-Pin Printers

Overview

Your printhead has one column of pins. Images are created as the pins "fire," striking the
ribbon against the paper to produce dots. White spaces appear where the pins don't fire. In 8-
pin graphics, each column of dots is represented by a single byte of data. In the Epson LQ
mode, Models ML390 Turbo, ML391 Turbo, ML590 and ML591 support 24-pin graphics, in
which each dot column is represented by three bytes of data.
When you program a graphic image, your program has to describe the pattern of dots you want
to print. Graphics data, like all other data sent to the printer, consists of a series of bytes. Each
of the eight bits in a byte of graphics data corresponds to one pin on the printhead. A bit's
value can be either 1 or 0. When the printer receives the data, it interprets a bit with a value of
1 as a command to fire the corresponding pin. Bits that are set to 0 don't cause pins to fire.
You can picture the byte as a column of 8 bits. In 8-pin graphics, the body of data is a series of
these columns lined up next to each other. Instead of sending the data to the printer bit by bit,
you'll probably want to convert this binary information into decimal or hexadecimal format for
use with your programming language. In the figure below we show how to determine the
decimal value for a given pattern of pins. For 24-pin graphics, you must perform this process a
total of three times.
Chapter 7: Graphics Commands for 24-Pin Printers 61