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INTEGRATED CIRCUITS 401

IC body

Pins or
"legs"
Figure 31- 19 Integrated circuits come
in a plastic rectangular body, with four or
Index or
clock mark more connection pins, or legs. A printed
index mark or notch shows the “top” of the
Pin #1 component. Pin 1 is always the first pin
when going counterclockwise.

Integrated circuits are enclosed in a variety of packages. The actual integrated circuit itself
is just a tiny sliver inside this package. For the hobbyist, the easiest- to- use IC package is the
dual in- line package (or DIP), like the one in Figure 31- 19. The illustration shows an 8- pin
DIP, but other sizes are common, too.

IDENTIFYING INTEGRATED CIRCUITS
As with transistors, ICs are identified by a unique code printed on the top. Codes may be a
simple number sequence such as 7400 or 4017. This code indicates a type of device that is
made by many different manufacturers. You can use this code to look up the specifications of
the IC in a reference book.
More than likely, the number identifying the IC will contain letters that further distinguish
it from other ICs of the same family, that is, ICs that do pretty much the same thing but have
different operating characteristics or manufacturing technologies. The differences among
these IC families are quite complex and well outside of what this book is about, but to get you
started, let’s take the 7400 as an example.
The 7400, which dates back to the swingin’ 1960s, contains four digital NAND gates;
NAND gates are one of several common forms of logic circuits used to create computers.
Variations of this chip include:
• 7400—Base chip as originally manufactured.
• 74ALS00—Advanced low- power Schottky; enhanced lower- power version.
• 74HCT00—CMOS version of the 7400 compatible with older devices.
And there are many others. When a circuit specifies just the base chip— the 7400 rather than
a specific family member— it usually means that the circuit isn’t particularly picky, and you can
use most any IC in that family.
Many ICs also contain other written information, including manufacturer catalog number
and date code. Do not confuse the date code or catalog number with the code used to identify

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