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

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Apparatus required:-The following electronics components are required.
•EX-OR Gate (IC-7486)
•AND Gate (IC-7408)
•OR Gate (IC-7432)
•NOT Gate (IC-7404)
•NAND Gate (IC-7400)
•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 Excess-3 to BCD Converter:-

K-Map for A: -                                  A = X1X2+X4X3X1
K-Map for B: -

K-Map for C: -

K-Map for D: -                        D=Bar(X4)

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. wrong truth table....

  2. Anonymous08 June, 2014

    Yo hav giiven a wrong truth table....
    please correct it....:(

  3. absolutely wrong

  4. which kind of K-map is that?

  5. Common, left hand side of truth table is not excess 3