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To Implementation of BCD to Excess-3 conversion using Logic gates.

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Apparatus required:-The following electronics components are required.
•XOR Gate (IC-7486)
•AND Gate (IC-7408)
•OR Gate (IC-7432)
•NOT Gate (IC-7404)
•Digital Trainer KIT
•Connecting wires
The availability of large variety of codes for the same discrete elements of information results in the use of different codes by different systems. A conversion circuit must be inserted between the two systems if each uses different codes for same information. Thus, code converter is a circuit that makes the two systems compatible even though each uses different binary code.
The bit combination assigned to binary code to gray code. Since each code uses four bits to represent a decimal digit. There are four inputs and four outputs. Gray code is a non-weighted code.
The input variable are designated as B3, B2, B1, B0 and the output variables are designated as C3, C2, C1, Co. from the truth table, combinational circuit is designed. The Boolean functions are obtained from K-Map for each output variable.
A code converter is a circuit that makes the two systems compatible even though each uses a different binary code. To convert from binary code to Excess-3 code, the input lines must supply the bit combination of elements as specified by code and the output lines generate the corresponding bit combination of code. Each one of the four maps represents one of the four outputs of the circuit as a function of the four input variables.
A two-level logic diagram may be obtained directly from the Boolean expressions derived by the maps. These are various other possibilities for a logic diagram that implements this circuit. Now the OR gate whose output is C+D has been used to implement partially each of three outputs.
Logic Diagram for BCD to Excess-3 Converter:-

K-Map for E3:-                            E3 = B3 + B2 (B0 + B1)

K-Map for E2:-
K-Map for E1:-
K-Map for E0:-                                   E0=Bar (B0)

Conclusion: - All the output verified the result of Truth Table.
Precaution in lab:-
•All the connections should be tight and proper.
•Handle the ICs carefully.
•Check the connection once again before Switching on the Digital Trainer KIT.
•Switch of the Trainer Kit after performing the Experiment.


  1. why cant u done by taking nand gates

  2. Yes it would be helpful if you can explain how the circuit looks like when realized using NAND gates.

  3. thank you very much ........ very useful ......... from a KIIT student (y)

  4. thanks ,it was helpful

  5. Sorry for my ignorance, But BCD exists upto 9 only, right?

  6. BCD has values upto 9 only then y did u took 10,11,12,13,14,15 in BCD TRUTH TABLE???