Epson FX-80 User Manual page 313

The hex mode prints 20 characters per line. If less than 20 characters
are sent, the printer sits in a holding pattern, awaiting more data.
Taking the printer off line will dump these characters to the paper.
The hex mode can be very useful in debugging a program. Just place
the printer in hex mode, RUN the program, and the printer will show
you exactly what it is receiving.
Problem Codes
Once you've determined the problem codes peculiar to your sys-
tem, either by using the hex test above or by trial and error, you can
start overcoming them.
Because each computer has a different set of problem codes, it is not
possible, in one short appendix, to provide solutions for all the com-
puters out there. But we can point out possible ways for you to solve
your problems.
There are generally two approaches. First, most computers can
avoid problem codes by sending each code directly to the printer. This
bypasses the BASIC interpreter and avoids the interface (where most
of the problems lie).
Unfortunately, this process is also different for each computer. We'll
take a stab at a couple here; if yours is not one of them, don't worry.
Remember that the concept is the same; consult your computer's man-
ual to determine if you can do the same on your system.
A second approach is to change the printer driver program in your
system. This requires a knowledge of machine language and of the
way your computer works. We show a sample driver below. The idea
behind a new printer driver is to pass the codes (as issued by a BASIC
program) directly to the printer rather than intercept and possibly
change them on the way through your computer.
We show examples of both methods below. Perhaps you can adapt
the ideas to your system.
POKEing Codes
The TRS-80 Model I version of the CHR$ function does not cor-
rectly pass on the values of 0, 10, 11, and 12. Zero is a particular
problem as it is very important to the ESC codes of the FX-80 yet is
totally ignored by the TRS-80.
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