Shopping List: Experiments 16 Through 24
148 Chapter 4
FundAmentAls
Choosing chips
Figure 4-2 shows what is often referred to as an integrated
circuit (IC). The circuit is actually etched onto a tiny wafer or
“chip” of silicon, embedded in a black plastic body, which is
properly referred to as the “package.” Tiny wires inside the
package link the circuit with the two rows of pins on either
side. Throughout this book, I will use the word “chip” to refer
to the whole object, including its pins, as this is the most
common usage.Figure 4-2. An integrated circuit chip in Plastic Dual-Inline Pin
package, abbreviated PDIP, or, more often, DIP.The pins are mounted at intervals of 1/10 inch in two rows
spaced 3/10 inch apart. This format is known as a Plastic
Dual Inline Package, abbreviated PDIP, or, more often, just
DIP. The chip in the photograph has four pins in each row;
others may have many more. The first thing you need to
know, when shopping for chips, is that you’ll only be using
the DIP package. This book will not be featuring the more
modern type, known as “surface-mount,” because they’re
much smaller, more difficult to handle, and require special
tools that are relatively expensive. Figure 4-3 shows a size
comparison between a 14-pin DIP package and a 14-pin
surface-mount package. Many surface-mount chips are
even smaller than the one shown.
Just about every chip has a part number printed on it. In
Figure 4-2, the part number is KA555. In Figure 4-3, the DIP
chip’s part number is M74HC00B1, and the surface-mount
chip is a 74LVC07AD. You can ignore the second line of
numbers and/or letters on each chip, as they are not part of
the part number.
Notice in Figure 4-3 that even though the chips look quite
different from each other, they both have “74” in their part
numbers. This is because both of them are members of the
“7400” family of logic chips, which originally had part numbers
from 7400 and upward (7400, 7401, 7402, 7403, and so on).Often they are now referred to as “74xx” chips, where “xx”
includes all the members of the family. I’ll be using this fam-
ily a lot, so you need to know how to buy them. I’ll give you
some advice on that without going into details yet about
what the chips actually do.Figure 4-3. The DIP chip, at the rear, has pins spaced 1/10
inch apart, suitable for insertion in a breadboard or perfo-
rated board. It can be soldered without special tools. The
small-outline integrated circuit (SOIC) surface-mount chip
(foreground) has solder tabs spaced at 1/20 inch. Other
surface-mount chips have pins spaced at 1/40 inch or even
less (these dimensions are often expressed in millimeters).
Surface-mount chips are designed primarily for automated
assembly and are difficult to work with manually. In this photo,
the yellow lines are 1 inch apart to give you an idea of the scale.Take a look at Figure 4-4, which shows how to interpret a
typical part number in a 74xx family member. The initial
letters identify the manufacturer (which you can ignore,
as it really makes no difference for our purposes). Skip the
letters until you get to the “74.” After that, you find two more
letters, which are important. The 74xx family has evolved
through many generations, and the letter(s) inserted after
the “74” tell you which generation you’re dealing with. Some
generations have included:- 74L
- 74LS
- 74C
- 74HC
- 74AHC
And there are more. Generally speaking, subsequent gen-
erations tend to be faster or more versatile than previous
generations. In this book, for reasons I’ll explain later, we are
mostly using the HC generation.