The synthesis of a switching circuit — i.e., its design or development — is started by stating or specifying what the circuit is supposed to do. We first briefly discuss the cumbersome plain prose specification, but it quickly becomes clear that more refined methods are needed. In fact one often employs specialised specification methods which are adapted to the type of problem under consideration. For instance, combinational circuits — the name used for circuits that are said to have no memorising capability — are advantageously specified in a table of asserted events (introduced in Section 3), or in so-called Karnaugh maps (discussed in Chapter 6). These two methods have neither the means of depicting the flow of time nor a succession of events, either of which is needed to specify a circuit with memorising capabilities — a sequential circuit.
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