Having considered some of thegeneralities of microcomputer hardwareand software in previous articles, andalso some parts of a particular practicalsystem, this six-part series concludes bylooking more closely at the centralprocessing unit — in this case the Z80microprocessor. Although some of thefollowing information has been given inprevious articles (November andDecember 1 97 7; January, February andAugust 1 978), it is being repeated herefor completeness and greater detail.A BLOCK DIAGRAM of the internalarchitecture of the Z80 central proces-sing unit is shown in Fig. 1. The diagramshows the major elements in the c.p.u.and it should be referred to throughoutthe following description. First let uslook at the c.p.u. registers. The Z80c.p.u. contains 208 bits of read/writememory that are accessible to the pro-grammer. Fig. 2 illustrates how thismemory is arranged into eighteen 8-bitregisters and four 16-bit registers. Theregisters include two sets of six generalpurpose registers that may be usedindividually as 8-bit registers or in pairsas 16-bit registers
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