Service manual

45
Non - E - proms
There are also some plastic encapsulated " Eproms" which can't be erased. These are
known as One Time Programmable (OTP) Eproms and can be somewhat cheaper than the
standard type, since you don't pay for a ceramic housing with a quartz window.
Obviously, it's no use buying these second hand! The programming time for these can be
seconds, rather than minutes. They are ideal for high volume production, but of little use to
the experimenter.
Unr ea d a bl e D e vic e s
There is another type of Eprom which results from incorrect programming voltage or,
especially, from being plugged into its socket the wrong way round. This device is known
as the T otally U nR eadable D evice, or TURD, and should be placed pins uppermost upon
your chair to remind you to be more careful next time.