Digital logic gate circuits are manufactured as integrated
circuits: all the constituent transistors and resistors built on a single
piece of semiconductor material. The engineer, technician, or hobbyist using
small numbers of gates will likely find what he or she needs enclosed in a
DIP (Dual Inline Package) housing. DIP-enclosed
integrated circuits are available with even numbers of pins, located at
0.100 inch intervals from each other for standard circuit board layout
compatibility. Pin counts of 8, 14, 16, 18, and 24 are common for DIP
"chips."
Part numbers given to these DIP packages specify what type of gates are
enclosed, and how many. These part numbers are industry standards, meaning
that a "74LS02" manufactured by Motorola will be identical in function to a
"74LS02" manufactured by Fairchild or by any other manufacturer. Letter
codes prepended to the part number are unique to the manufacturer, and are
not industry-standard codes. For instance, a SN74LS02 is a quad 2-input TTL
NOR gate manufactured by Motorola, while a DM74LS02 is the exact same
circuit manufactured by Fairchild.
Logic circuit part numbers beginning with "74" are commercial-grade TTL.
If the part number begins with the number "54", the chip is a military-grade
unit: having a greater operating temperature range, and typically more
robust in regard to allowable power supply and signal voltage levels. The
letters "LS" immediately following the 74/54 prefix indicate "Low-power
Schottky" circuitry, using Schottky-barrier diodes and transistors
throughout, to decrease power dissipation. Non-Schottky gate circuits
consume more power, but are able to operate at higher frequencies due to
their faster switching times.
A few of the more common TTL "DIP" circuit packages are shown here for
reference:
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