What is a Code Converter?

A Code Converter is a combinational digital circuit that transforms data represented in one binary code into another binary code without changing the numerical value or meaning of the data.

• The meaning remains the same, only the representation changes.

Similarly:

0101_Binary = 0101_BCD = 1000_Excess−3

Different codes → Same value → Converted by a Code Converter.

• It does not store information (no memory element).
• Output depends only on present input.
• Widely used in digital systems, communication, displays, and processors.

Why Do We Need Code Conversion?

Different digital subsystems use different coding schemes. To make them communicate, we must convert codes.

Example: A digital clock internally works in binary, but the display needs BCD → 7-segment conversion.

Table of Code Converter Circuits

Steps to Design a Code Converter Circuit

• Designing a Code Converter means creating a combinational logic circuit that translates one code into another while preserving the same numerical meaning.
• The design process follows a systematic digital design methodology similar to designing any combinational circuit.

Step-1: Clearly Define the Conversion Requirement

First, identify:

• Input Code → Which code is given?
• Output Code → Which code is required?
• Number of Bits involved.

Example: Design a converter to transform 4-bit Binary → Gray Code.

Input Variables: B3​, B2​, B1​, B0​

Output Variables: G3, G2, G1, G0

Step-2: Construct the Truth Table

• List all possible input combinations and write their corresponding output code values.
• This step establishes the functional relationship between input and output.

Example: Truth Table of 4-bit Binary → Gray code converter. A 4-bit system has 2⁴ = 16 possible combinations.

Step-3: Derive Boolean Expressions for Each Output Bit

Each output bit is treated as a separate Boolean function of the input variables.

G₃​=f(B₃​, B₂​, B₁​, B₀​)

G₂​=f(B₃​, B₂​, B₁​, B₀​)

G₁​=f(B₃​, B₂​, B₁​, B₀​)

G₀​=f(B₃​, B₂​, B₁​, B₀​)

From the truth table, determine where each output is 1 and form the Sum-of-Minterms expression.

Step-4: Simplify Using Karnaugh Maps (K-Map)

K-Map minimization is essential to:

• Reduce hardware complexity
• Minimize number of gates
• Increase speed and efficiency

For each output variable, draw a K-Map and group the 1’s.

Step-5: Implement the Logic Circuit

Using the simplified Boolean equations, draw the final logic diagram using gates such as:

• • AND
  • OR
  • NOT
  • XOR (very common in code converters)

Step-6: Verify the Design

Verification ensures the converter works correctly.

Methods:

• • Recheck truth table with derived equations.
  • Simulate using:
    • Logic simulator (Multisim / Logisim)
    • HDL simulation (Verilog/VHDL)

Example Check:

Input:  B₃ B₂ B₁ B₀ = 1 0 1 1

Output: G₃ G₂ G₁ G₀ = 1 1 1 0

Value remains the same → conversion successful.