H Hex Dumping And Problem Codes - Epson FX-80 User Manual

AppendixH
Hex Dumping and Problem Codes
The Seven-Bit
Limitation
BASIC programs on the Apple II Plus (and perhaps some other
computers) can send to the printer only 7 bits at a time instead of the
normal 8 (machine-language programs can send 8). Because of this
limitation, the CHR$ function on these computers is unable to deliver
the entire range of ASCII codes (0 - 255) to the printer; it can send only
the codes 0 -127. The FX-80 can interpret these codes as either 0 -127
or as 128 - 255-but not as both ranges at once. The low range is
automatically active unless the high range is set by the user.
The computer converts all codes outside of the active range to their
equivalent active range code by adding or subtracting 128.
The following simple test can be used to determine the status of
your computer:
1~ FOR X=16~ TO 254
2~
LPRINT CHR$(X);
3~
NEXT X
If you get italic characters when you RUN this, your system is capable
of generating all 256 ASCII codes (it's an B-bit system). If you get
standard roman characters, then your system is forcing all codes into
the lower range; you should pay close attention to the following.
As you have discovered in this manual, the FX-80 sometimes re-
quires fu1l8-bit capability. Users of 7-bit computers will have to find
ways to cope with these situations.
In
most cases, the 7-bit limitation
is not totally debilitating, but rather more of an annoyance. Often you
can achieve the same results as 8-bit users can, but it takes a little more
coding or manipulating of the high-order bit.
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