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Fig. 1, Functional symbols of two logic blocks. Bottom lead of the flip-flop is P.

Micro-Ultimatic. The logic line is available from many distributors (discussed later).

Since the digital IC is a complete logic package we don't really have to know what goes on inside in order to assemble a system. So first, let's quickly review the fundamentals of a binary digital system.

A binary system is one in which there are only two recognized states. In a typical electronic system, a voltage is associated with each of these states. The states, or levels, are variously called "true" and "false/' 'T' and "0," "high" and low/' etc. We may choose the terms we want to use. For our purposes here, the terms "high" and "low," I think, help convey more of a physical meaning, since we can associate each with a voltage, one high and one low.

At any instant of time in a binary system the state at any point is either high or low. li; it is not one, it is the other. Here we ignore the quite practical fact that in a reallife system some high states may be higher than others. Further, the state at some point in a system is usually the result of the states of one or more points elsewhere in the system, The exact relation between the inputs and outputs of one block of the system is frequently expressed by Boolean algebra, but we can understand the concept by other means.

The NAND Gate

A very useful logic block in a system is the NAXD gate. It can be represented func-

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