Page 31 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Digital Circuits and Logic Design

Notes
Figure 2.14: How to Expand the Number of Inputs of a NOR Gate

You can also easily transform NAND and NOR gates into an inverter by shorting their inputs,
like shown in Figure 2.15. This is a very common trick. For example, you need an inverter in your
circuit and have some NOR or NAND gates available at a given integrated circuit. Instead of adding
another integrated circuit to your project just to have one inverter (what would increase the final
circuit size and also the cost), you may want to use one of the available NAND or NOR gates.

Figure 2.15: Transforming a NOR Gate into an Inverter

The most famous NOR gate integrated circuit is 7402 and you can its pinout in Figure 2.16. Pay
attention because the location of the inputs and outputs on this integrated circuit is different from
the other integrated circuits we have seen before. Of course there are several other integrated
circuits that neither provide NOR gates with more inputs. For example, 7427 provides three
three-input NOR gates.
Figure 2.16: 7402 Integrated Circuit Provides Four Two-Inputs NOR Gates

Implement a 2-input AND gate using NAND gate only and implement a 2-input
AND gate using NOR gates only.
Self Assessment

Choose the correct answer:
1. The output of a logic gate is 1 when all its inputs are at logic 0 the gate is either ................. .
(a) a NAND or an EX-OR (b) an OR or an EX-NOR
(c) an AND or an EX-OR (d) a NOR or an EX-NOR

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