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MC14XXXBD датащи(PDF) 7 Page - Motorola, Inc |
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MC14XXXBD датащи(HTML) 7 Page - Motorola, Inc |
7 / 13 page MOTOROLA CMOS LOGIC DATA 7 MC14560B The truth table and Karnaugh maps for sign, overflow, and End Around Carry are shown in Figures 6 and 7. Note the use of BS′ from the exclusive–OR of Add/Sub and BS. BS′ eliminates Add/Sub as a variable in the truth table. As an ex- ample of truth table generation, consider an n decade adder/ subtracter where AS = “0”, BS = “1”, and Add/Sub = “0”. B is in 9’s complement form, 10N – 1 – B. Thus A + (10N – 1 – B) = 10N – 1 + (A – B). There is no carry when A v B, and the sign is negative (sign = “1”). When AS and BS are opposite states and Add/Sub is a “0” (add mode), no overflow can oc- cur (overflow = “0”). The other output states are determined in a similar manner (see Figure 6). From the Karnaugh maps it is apparent that End Around Carry is composed of the two symmetrical functions S2 and S3 of three variables with AS BS′ Cout as the center of sym- metry. This is the definition of the majority logic function M3(ABC). Similarly the Sign is composed of the symmetrical functions S2(3) and S3(3) but with the center of symmetry translated to ASBS′ Cout. This is equivalent to the majority function M3(ASBS′ Cout). Further evaluation of the maps and truth table reveal that Overflow can be generated by the exclusive–OR function of End Around Carry and Carry Out. This analysis results in a minimum device count consisting of one exclusive–OR package and one dual Majority Logic package to implement BS′, EAC, Sign and Overflow. The logic connections of these devices are shown in Figure 5. The output sign, RS, complements the result of the add/ subtract operation when RS = “1”. This is required because the adder performs 9’s complement arithmetic. Complement- ing, when RS indicates the result is negative, restores sign and magnitude convention. Several variations of the adder/subtracter are possible. For example, 9’s complement is available at the output of the NBCD adders, and output complementers are eliminated if sign and magnitude output is not required. Figure 6. Subtraction of Unsigned NBCD Numbers A B VDD Z C C A1 A2 A3 A4 F1 F2 F3 F4 Cn Cin A1 A2 A3 A4 B1 B2 B3 AB Cout Cn + 1 S1 S2 S3 S4 MC14560 A1 A2 A3 A4 Z C C VDD F1 F2 F3 F4 MC14561 FROM Cout OF MOST SIGNIFICANT DECADE RESULT, R LEAST SIGNIFICANT DECADE A1 B1 A2 B2 An Bn MOST SIGNIFICANT DECADE Cin C Cout Cin C Cout Cin C Cout R1 R2 Rn “0” INDICATES UNDERFLOW (NEGATIVE RESULT) (a) Basic Subtracter Block (b) n–Decade Subtracter Typical Subtract Time = 0.6 + 0.4n µs where n = Number of Decades MC14561 BASIC SUBTRACT BLOCK R1 |
Аналогичный номер детали - MC14XXXBD |
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Аналогичное описание - MC14XXXBD |
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