LOGIC FAMILIES

3-38 Q58. How many clock pulses are required to output a 4-bit number in serial form? Q59. Two shifts to the left are equal to increasing the magnitude of a number by how much? Q60. To increase the magnitude of a number by 2³, you must shift the number how many times and in what direction? LOGIC FAMILIES Logic families are groups of logic circuits that are based on particular types of elements (resistors, transistors, and so forth). Families are identified by the manner in which the elements are connected, and, in some cases, by the types of elements used. Logic circuits of a particular family can be interconnected without having to use additional circuitry. In other words, the output of one logic circuit can be used as the input to another logic circuit. This feature is known as compatibility. All circuits within a logic family will be compatible with the other circuits within that family. As a technician, your responsibility will be to identify defective parts and repair or replace them as required. It will be beneficial for you to have a basic knowledge of the types of logic that are used in digital equipment. Logic circuits are usually manufactured as integrated circuits and packaged in dual-inline packages (DIP), modified transistor outlines (TO), or flat packs. These packaging techniques are described in NEETS, Module 7, Introduction to Solid-State Devices and Power Supplies. Circuitry in a package is normally shown using standard logic symbols instead of individual components such as transistors, diodes, and so forth. Figure 3-34 shows four examples of this type of packaging. The numbered blocks (1-14 and 1-16) are the pins on the package. Circuit packages are also identified by a manufacturer’s part number. Similar circuits produced by different manufacturers will not carry the same identification numbers in all cases.