Table of Contents
Advertisement
If the printer beeps and stops printing when it is not out of paper,
turn the printer off and check to see if the paper is loaded correctly. If
the paper is loaded correctly, turn the printer back on and try to print
again. If the printer beeps and does not print again, take it to a
qualified service person.
Problem Codes
Sending certain codes from the Apple IIc to the printer can present
problems. There are two reasons for these problems:
1. The Apple operating system is set up to handle seven-bit numbers,
but the LX-90 can handle eight-bit numbers.
2. The Apple uses a few of the low-numbered codes, especially num-
bers 4 and 9, for special purposes. Therefore, some LX-90 pro-
grams, especially graphics programs, must be written so that these
special purposes do not interfere with the output of the LX-90 pro-
gram.
Computers and printers do not use the decimal number-
ing system that you are familiar with. Instead they use the
binary numbering system, in which all numbers are repre-
sented by combinations of the digits 0 and 1 instead of the
10 digits that the decimal system uses. For example, the
binary number 01001011 is equivalent to the decimal num-
ber 75.
You do not need to understand the binary system to use
your printer or to understand this appendix. Just be aware
t h a t s e v e n - b i t b i n a r y n u m b e r s a r e e q u i v a l e n t t o d e c i m a l
numbers from 0 to 127 and that eight-bit binary numbers
a r e e q u i v a l e n t t o d e c i m a l n u m b e r s f r o m 0 t o 2 5 5 . T h e r e -
fore, making the eighth bit equal to zero is the same as sub-
t r a c t i n g 1 2 8 f r o m a n y d e c i m a l n u m b e r a b o v e 1 2 7 .
The operating system of the Apple IIc normally sends codes with
the eighth bit equal to one and assumes that the printer will ignore the
eighth bit. Therefore, in the standard mode (when DIP switch 2-2 is
OFF) the Apple IIc PIC makes the eighth bit equal to zero so that it will
not interfere with any of the printer instructions. In decimal terms,
this means that it subtracts 128 from any number above 127.
About bits . . .
E-5
Hide quick links:
Advertisement
Table of Contents
