Digital Electronics: Principles, Devices and Applications

Arithmetic Circuits 253Figure 7.27 Solution to example 7.4.ABXYFigure 7.28 Example 7.5.Example 7.6Design a BCD adder circuit capable of adding BCD equivalents of two-digit decimal numbers. Indicatethe IC type numbers used if the design has to be TTL logic family compatible.SolutionThe desired BCD adder is a cascaded arrangement of two stages of the type of BCD adder discussedin the previous pages. Figure 7.29 shows the logic diagram, and it follows the generalized cascadedarrangement discussed earlier and shown in Fig. 7.22 for a three-digit BCD adder. The BCD adderof Fig. 7.21 can be used to add four-bit BCD equivalents of two single-digit decimal numbers. Acascaded arrangement of two such stages, where the output C of Fig. 7.21 (CARRY-OUT) is fed tothe CARRY-IN of the second stage, is shown in Fig. 7.29. In terms of IC type numbers, IC 7483 canbe used for four-bit binary adders as shown in the diagram, IC 7408 can be used for implementing