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Full Subtractor

October 18, 2018



A full subtractor may be a combinatory circuit that performs subtraction of 2 bits, one is number and different in number, taking under consideration borrow of the previous adjacent lower number bit. thus there square measure 3 bits square measure thought-about at the input of a full subtractor. There square measure 2 outputs, that square measure distinction output D and BORROW output, Bo.

The BORROW output indicates that the number bit needs to borrow ‘1’ from the following number bit. The figure shows the reality table of a full subtractor. the 2 outputs, D and Bout represent the distinction and output borrow, severally.



Full-subtractor-Block-Diagram

       Fig: Full subtractor Block Diagram

Block Diagram

Hence there square measure 3 bits square measure thought-about at the input of a full subtractor. There square measure 2 outputs, that square measure distinction output D and BORROW output B. The BORROW output indicates that the number bit needs to borrow ‘1’ from subsequent number bit. The 3 inputs square measure X, Y, and Z denotes the number, subtrahend, and therefore the previous borrow, severally. the 2 outputs, D and Bout represent the distinction and output borrow, severally.

Symbol

Full-subtractor-Symbol

Fig: Full subtractor Symbol

If we have a tendency to compare distinction output D and BORROW output Bo with full adder`it is seen that the distinction output D is that the same as that for the added output. Further, the BORROW output Bo is comparable to CARRY-OUT. we have a tendency to aforementioned before that the sole distinction between a full adder and a full subtractor was the inversion of 1 of the inputs.

 

 



Truth Table

Full-sub-Truth-Table

Fig: Full sub-Truth Table

 

As with the binary adder, we will even have n variety of 1-bit full binary cypher connected or “cascaded” along to subtract 2 parallel n-bit numbers from one another. for instance 2 4-bit binary numbers. the method of subtraction becomes Associate in Nursing addition as we will use two’s complement notation on all the bits within the number and setting the carry input of the smallest amount vital bit to a logic (HIGH).