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Left-to-right printing
The EX-800 normally prints bidirectionally, with the print position moving
alternately left-to-right and right-to-left. Cutting down printhead motion
does speed up printing for those earlier styles of printer- though it hardly
compares with laser printing.
The problem with bidirectional printing is that the printhead can get slightly
out of alignment. When you’re using more primitive tools sometimes
accuracy matters more than speed, so a command for plain old left-to-right
printing (sometimes called “unidirectional printing”) is available on Epson’s
printers.
The following command does nothing to improve the accuracy of your Star
LaserPrinter 8111, but it’s included for software compatibility’s sake. The
command just moves the print position to the left margin, acting as a carriage
return without a line feed. Normal printing resumes with the next carriage
return.
To turn on left-to-right printing for just one line, this is the command:
<ESC> <
Moving horizontally from the left margin
Two horizontal motion commands send the print position to a particular
position on the line. These commands are based on EX-800 dots. Unfortu-
nately the EX-800 offers only 60 or 120 dots per inch, rather than the Star
LaserPrinter 8III’s usual density of 300 dots. So we’ll express these moves
in terms of increments of l/60 or l/120 inch.
One move command is an “absolute’* move, to the right from the left margin.
The other is a “relative” move, left or right from the current print position.
To move from the left margin in increments of l/60 inch, you send this
command:
<ES0 $ nl n2
At the beginning of the chapter we said some command variables, like nl and
n2 here, could represent bytes to be added together. This is one of those
commands. The nl represents units and n2 represents 256-unit groups. In this
move command, the actual units are the l/60 inch increments.
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