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Electronic Labs_80

Electronic Labs_80 - 4-2 Dual Gating Functions Symbolic...

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Unformatted text preview: 4-2 Dual Gating Functions, Symbolic Notation and Practical Gate Applications Now that we have seen the same circuit can perform different or dual logic functions, we must pro— vide a means for circuit analysis. We would show the 'AND function with truth table as in Fig. 4-2a and the OR function with truth table in Fig. 4—2b. "MW Y (#1 n I I . 3)— lb) Fig. 4-2 Note that the integrated circuit identified by the 7408 number and the truth tables are identical. The circuit function of Fig. 4-2a is the AND function symbol and the absence of circles at inputs and outputs indicate that when A and B are HI then Y is HI. The circuit function of Fig. 4-2b is the OR function, the symbol is the OR func- tion symbol and the presence of circles at the inputs and outputs indicate that when A or B or both are LO then Y is L0. The dual symbols for each gate are given in Table 4-1. Again, note that the truth tables are identical for the dual pairs. The logic functions differ as indicated by the logic symbols and the input! output states. Note that an input A shown in the symbol without a circle is indicated A for the circuit function and the truth table shows A must be 1. Similarly, input A shown in the symbol with a circle is indicated as A for the circuit func- tion and the truth table shows A must be 0. This also follows for B and Y in the table. Symbolic notation and gate applications will become more clear as we discuss practical decision making circuits. Additional Reading See the bibliography in the back of this manual for additional reading material on logic gates, dual functions and complementary inputs. Yis‘lwhenAorBis‘I Y=A+B Yis‘lwhenAandBareO A Y=A-§ V=A YislwhenAISO Y=A NOTE: A, B AND Y ARE (LO) WHERE INDICATED BY CIRCLES TO OBTAIN THE INDICATED SYMBOLIC FUNCTION: Table 4-1 Equipment and Materials The Model ASl8145 Digital Logic Trainer with: - Hex Inverters (7404) - 2-input NAND Gates (7 400) - 4-input NAND Gates (7420) 2-input AND Gate (7408) - 2-input OR Gates (7432) - Switches - LED Displays Niacin—4min». I Objective A. Determine the logic states and gating functions required for a MAJORITY VOTE sys- tem and verify that the proper logic decisions are made. Preparatory Information. The circuit shown in Fig. 4-3 may be used to determine if a majority of voters has voted “FOR” or “AGAINST” a particular issue. For simplicity, we will only con- cern ourselves with three voters (A, B, C) and any ...
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