BCD stand for binary coded decimal. Suppose, we have two 4-bit numbers A and B. The value of A and B can varies from 0(0000 in binary) to 9(1001 in binary) because we are considering decimal numbers.
The output will varies from 0 to 18, if we are not considering the carry from the previous sum. But if we are considering the carry, then the maximum value of output will be 19 (i.e. 9+9+1 = 19).
When we are simply adding A and B, then we get the binary sum. Here, to get the output in BCD form, we will use BCD Adder.
Input : A = 0111 B = 1000 Output : Y = 1 0101 Explanation: We are adding A(=7) and B(=8). The value of binary sum will be 1111(=15). But, the BCD sum will be 1 0101, where 1 is 0001 in binary and 5 is 0101 in binary.
Input : A = 0101 B = 1001 Output : Y = 1 0100 Explanation: We are adding A(=5) and B(=9). The value of binary sum will be 1110(=14). But, the BCD sum will be 1 0100, where 1 is 0001 in binary and 4 is 0100 in binary.
Note – If the sum of two number is less than or equal to 9, then the value of BCD sum and binary sum will be same otherwise they will differ by 6(0110 in binary).
Now, lets move to the table and find out the logic when we are going to add “0110”.
We are adding “0110” (=6) only to the second half of the table.
The conditions are:
- If C’ = 1 (Satisfies 16-19)
- If S3′.S2′ = 1 (Satisfies 12-15)
- If S3′.S1′ = 1 (Satisfies 10 and 11)
So, our logic is
C' + S3'.S2' + S3'.S1' = 1
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- Difference between Serial Adder and Parallel Adder
- Difference between Half adder and full adder
- Half Adder in Digital Logic
- Full Adder in Digital Logic
- Serial Binary Adder in Digital Logic
- Difference between Programmable Logic Array and Programming Array Logic
- Half Adder and Half Subtractor using NAND NOR gates
- Carry Look-Ahead Adder
- Parallel Adder and Parallel Subtractor
- 4-bit binary Adder-Subtractor
- Half Subtractor in Digital Logic
- Counters in Digital Logic
- Synchronous Sequential Circuits in Digital Logic
- Multiplexers in Digital Logic
- Full Subtractor in Digital Logic
- Binary Decoder in Digital Logic
- Encoder in Digital Logic
- Functional Completeness in Digital Logic
- Ripple Counter in Digital Logic
- Shift Registers in Digital Logic
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