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the cable, the cable must be pushed onto the 40 pins so that the cable<br />
is pointed either down or away from the printed-circuit board. If the<br />
cable is connected improperly, the Apple will respond with a screen<br />
full of random characters rather than the APPLE II banner, when<br />
it is first turned on. This does not seem to cause any permanent dame<br />
age to the Apple or to the interface as long as they are not connected<br />
this way for too long.<br />
Some experiments will build on, or use, the circuits or<br />
developed in previous experiments. Please do not tum off power<br />
to the computer, and do not disconnect circuits until you are told<br />
do so, otherwise, you will spend a great deal of time reloading programs<br />
and reconstructing interface circuits. There will be a reminder<br />
at the end of some of the experiments just so that you don't forget<br />
this tip.<br />
Most readers will probably perform the experiments in sequence,<br />
so there will not be too much difficulty in referring back to previous<br />
experiments for the details of the interface circuits. However, if you<br />
choose to skip over some experiments you may find this a bit confusing.<br />
To help everyone with the interface circuits, we have reproduced<br />
the important input port, output port, and control circuits in<br />
Fig. 6-27 at the end of this chapter. You can make a photocopy of<br />
this figure, or you may remove it from the book so that it will be<br />
nearby when you need it. The basic circuits shown in this figure are
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