Filter
Top Products
Send it a Message
Chapter 2
Send it a Message
The MX-70 printer is smart. It knows how to follow instructons.
Any Code Devised by Man Can be Broken by Man
Many instructions are sent to the printer. Every letter, number, and other
character travels from the computer through the printer cable in the form of a
code made up of numbers. We know it as the ASCII code (American Standard
Code for Information Interchange), pronounced ASK-key.
Let’s take a quick glance at Appendix A to refresh our memory. The decimal
number 65 stands for the letter A - etc.
The ASCII code numbers for upper case letters, numbers, and punctuation are
pretty well standardized around the world. Unfortunately, the remaining code
numbers are used in a variety of different ways, even among manufacturers
within a single country.
Besides letters and numbers, we can also send “special” codes to make the
MX-70 print wide letters, or enter a special graphics mode that permits us to
control where each individual dot is printed. To take advantage of these fea-
tures, however, the comptuer has to be able to send these special code numbers.
As we will see, each with his own computer, not all computers can send all code
numbers. With printer technology advancing faster than computer technology,
the computer has replaced the printer as the weak link in the system.
The Code Courier
In many cases, the easiest way to send these special codes is to “build” them
into the computer program along with its “regular” codes for ordinary letters
and numbers. We can do this easily using programs written in the BASIC (or
another) computer language. Because of its simplicity and overwhelming popu-
larity, we will do all our demonstrating and learning here in BASIC.
We can also send these special codes at some computers “command level”
before running a program. A program may even contain codes to change earlier
codes, allowing us to print things the way we want them, when we want them.
The route to success in BASIC is via CHR$ (pronounced Character String).
Users with so-called Integer BASIC, which may not support the CHR$ func-
tion, may be restricted to very routine printing. To use the MX-70’s exotic
13