titus-larsen-titus-1981-apple-interfacing

CHAPTER
On the Bus
'While many readers will be content to perform some of the
ments in the previous chapter, and go no further with the design
development of interfaces, there are others who will be intpu•oh•.rl
in developing special-purpose interface circuits that will become
permanent part of their computer system. This chapter is written
this reader. We will describe how you can design special initerl::ace
circuits that can take advantage of many of the built-in features of
the Apple computer.
If you want to construct an interface circuit that will be used again
and again, you will want to construct it on something other than a
solderless breadboard. Breadboarded circuits take up workspace,
they are messy and frequently come apart at the worst possible moment.
The alternative is to construct the interface circuit in
permanent form, so that it can be mounted out of harm's way, inside
the Apple case.
When the Apple computer was designed, it must have been obvious
to the engineers that people would be interested in expanding
the system so that various standard peripherals and nonstandard circuits
could be added to the computer. Thus, they provided eight female
edge connectors at the rear of the main printed circuit board,
so that the important computer signals would be readily availab!e for
anyone who wanted to use them. You have already used some of
these signals, since the interface that was described previously plugs
into one of the available "slots."
The slots are numbered 0-7, and you can use all but slot 0, which
has been reserved by the manufacturer for special expansions of the
computer. Slots 1-7 are available for you to use as you wish. There