Although there are many ways of making integrated circuits, and several technologies are available to the manufacturer, two major ‘families’ of general-purpose logic ICs remain the most important. The first, and the oldest, family is TTL; TTL stands for Transistor-Transistor Logic, this logic family having replaced the older — now obsolete — DTL (Diode-Transistor Logic). The second logic family is CMOS (pronounced ‘sea-moss’) which stands for Complementary Metal-Oxide Semiconductor. Both families include a very large number of different devices: gates, flip-flops, counters, registers and many other ‘building-block’ elements. In many cases there are direct substitutes, but, as we shall see, it is not usually sensible to mix devices from the two families.
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