Digital Electronics: Principles, Devices and Applications

632 Digital ElectronicsTable 15.1 Example 15.2.Binary codeGray codeA 3 A 2 A 1 A 0 D 3 D 2 D 1 D 00 0 0 0 0 0 0 00 0 0 1 0 0 0 10 0 1 0 0 0 1 10 0 1 1 0 0 1 00 1 0 0 0 1 1 00 1 0 1 0 1 1 10 1 1 0 0 1 0 10 1 1 1 0 1 0 01 0 0 0 1 1 0 01 0 0 1 1 1 0 11 0 1 0 1 1 1 11 0 1 1 1 1 1 01 1 0 0 1 0 1 01 1 0 1 1 0 1 11 1 1 0 1 0 0 11 1 1 1 1 0 0 0AddressInputD 0A 3A 0 D 3A 2A 116 × 3ROMD 1D 2DataOutputFigure 15.21 Solution to problem 15.2.15.7 Expanding Memory CapacityWhen a given application requires a RAM or ROM with a capacity that is larger than what isavailable on a single chip, more than one such chip can be used to achieve the objective. The requiredenhancement in capacity could be either in terms of increasing the word size or increasing the numberof memory locations. How this can be achieved is illustrated in the following paragraphs with the helpof examples.15.7.1 Word Size ExpansionLet us take up the task of expanding the word size of an available 16 × 4 RAM chip from four bits toeight bits. Figure 15.22 shows a diagram where two such RAM chips have been used to achieve the