Exclusive OR Gate

The exclusive OR gate is a modified OR gate that produces a 1 output when only one of the inputs is a 1. The abbreviation often used is X-OR. It is different from the standard OR gate in that when both inputs are a 1, then the output remains at a 0. The standard symbol and truth table for the X-OR gate are shown in Figure 10-250.

Exclusive NOR Gate

The exclusive NOR (X-NOR) gate is nothing more than an X-OR gate with an inverted output. It produces a 1 output when all inputs are 1s and also when all inputs are 0s. The standard symbol is shown in Figure 10-251.

The Integrated Circuit

All of the logic functions so far discussed plus many other components are available in some form of an integrated circuit. The digital systems found in today’s aircraft owe their existence to a large extent to the design of the integrated circuit (IC). In most cases, the IC has an advantage over the use of discrete components in that they are smaller, consume less power, are very reliable, and are inexpensive. The most noticeable characteristic of the IC is its size and in comparison to the discrete semiconductor component, can easily be on the order of thousands of times smaller. [Figure 10-252]

A monolithic integrated circuit is an electronic circuit that is constructed entirely on a single chip or wafer of semiconductor material. All of the discrete components, such as resistors, transistors, diodes, and capacitors, can be constructed on these small pieces of semiconductor material and are an integral part of the chip. There are a number of levels of integration. Those levels are: small-scale integration, medium-scale integration, large-scale integration, and microprocessors. The small-scale integration is considered the least complex design of the digital ICs. These ICs contain the basic components such as the AND, OR, NOT, NOR and NAND gates. Figure 10-253 illustrates the schematic form of this type of circuit. The medium

scale integration can contain the same components as found in the small-scale design but in larger numbers ranging from 12 to 100. The medium-scale designs are house circuits that are more complex, such as encoders, decoders, registers, counters, multiplexers, smaller memories, and arithmetic circuits. Figure 10-254 illustrates the schematic form of this type of circuit. The large-scale integrated circuits contain even more logic

gates, larger memories than the medium-scale circuits, and in some cases microprocessors.

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