The parallel adder/subtractor performs the addition operation faster as compared to serial adder/subtractor. Time required for addition does not depend on the number of bits. The output is in parallel form i.e all the bits are added/subtracted at the same time. It is less costly. Disadvantages of parallel Adder/Subtractor –. Nov 02, 2017 VHDL code for an N-bit Serial Adder with Testbench code Normally an N-bit adder circuit is implemented using N parallel full adder circuits, simply connected next to each other. The advantage of this is that, the circuit is simple to design and purely combinatorial.
The serial binary adder or bit-serial adder is a digital circuit that performs binaryaddition bit by bit. The serial full adder has three single-bit inputs for the numbers to be added and the carry in. There are two single-bit outputs for the sum and carry out. The carry-in signal is the previously calculated carry-out signal. The addition is performed by adding each bit, lowest to highest, one per clock cycle.
Serial binary addition[edit]
Serial binary addition is done by a flip-flop and a full adder. The flip-flop takes the carry-out signal on each clock cycle and provides its value as the carry-in signal on the next clock cycle. After all of the bits of the input operands have arrived, all of the bits of the sum have come out of the sum output.
Serial binary subtracter[edit]
The serial binary subtracter operates the same as the serial binary adder, except the subtracted number is converted to its two's complement before being added. Alternatively, the number to be subtracted is converted to its ones' complement, by inverting its bits, and the carry flip-flop is initialized to a 1 instead of to 0 as in addition. The ones' complement plus the 1 is the two's complement.
Example of operation[edit]
Decimal
5+9=14
X=5, Y=9, Sum=14
Binary
0101+1001=1110
Addition of each step
4 Bit Adder Circuit
Inputs
Outputs
Cin
X
Y
Sum
Cout
0
1
1
0
1
1
0
0
1
0
0
1
0
1
0
0
0
1
1
0
*addition starts from lowest
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Result=1110 or 14
See also[edit]
References[edit]
Four Bit Adder Circuit
Further reading[edit]
External links[edit]
Interactive Serial Adder, Provides the visual logic of the Serial Adder circuit built with Teahlab's Simulator.
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