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CHAPTER<br />
Apple Interfacing<br />
At this point, you are probably wondering:<br />
® How does the Apple actually transfer information to<br />
vices<br />
(i:ll How are the I/ 0 devices actually synchronized to the operation<br />
of the computer<br />
How are individual I/O devices selected or identified<br />
®' How do I/ 0 devices place their data on the data bus and how<br />
do they actually receive it from the data bus<br />
These are important questions, since the answers to them will provide<br />
the basis for your understanding of microcomputer <strong>interfacing</strong>,<br />
We will be answering these questions in this and other chapters, 'lVe<br />
will also provide some experiments that will reinforce the concepts<br />
through hands-on experience,<br />
A few examples of digital circuits will be<br />
in this chapter,<br />
We have assumed that you can "read" interpret a circuit<br />
diagram, and that you are familiar with the more common SN7 400-<br />
series transistor-transistor logic (TTL) circuits<br />
Before we can discuss the actual transfer of information between<br />
I/O devices and the computer, we must first understand the circuitry<br />
and the signals that are used to identify or address the individual<br />
I/0 devices. There are many schemes that may be used and we will<br />
examine several of them, It is impossible to show possible<br />
scheme for addressing I/ 0 devices, since modifications be made<br />
to suit special needs.
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