Debug BCD Adder Correction Logic
A BCD (Binary-Coded Decimal) adder performs base-10 arithmetic by adding two 4-bit BCD digits and applying a correction factor of 6 when the initial binary sum exceeds 9.
Expected behavior:
The circuit accepts two 4-bit BCD inputs A and B (valid range 0 to 9) and a carry-in Cin. It produces a 4-bit BCD sum S and a BCD carry-out Cout.
Simulation shows S = 1 and Cout = 0 for inputs A = 8, B = 9, and Cin = 0. The expected output is S = 7 and Cout = 1. The adder produces incorrect results for specific high-value input pairs. Inspect the circuit and correct the fault.
Constraints
- Do not alter the initial 4-bit binary addition stage.
- Ensure the correction logic correctly identifies all cases where a +6 adjustment is required.
- Use standard combinational logic gates for the correction detection.
Topics
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