3-10Q12.What is the output of C_{1}?SUBTRACTIONSubtraction is accomplished in computers by the R’s complement and add method. This is the samemethod you used in chapter 1 to subtract binary numbers.R’s complement subtraction allows us to use fewer circuits than would be required for separate addand subtract functions. Adding X-OR gates to full adders, as shown in figure 3-11, enables the circuit toperform R’s complement subtraction as well as addition.Figure 3-11. —R's complement adder/subtracter.To add two numbers using this circuit, the addend and augend are applied to the A and B inputs. TheB inputs are applied to one input of the X-OR gates. A control signal is applied to the other input of theX-OR gates. When the control signal is LOW, the circuit will add; and when it is HIGH, the circuit willsubtract.In the add mode, the outputs of the X-OR gates will be the same as the B inputs. Addition takesplace in the same manner as described in parallel addition.Before we attempt to show subtraction, let’s review R’s complement subtraction. To subtract 10_{2}from 11_{2}, write down the minuend (11_{2}). Perform the R’s complement on the subtrahend. Now add theminuend and the complemented subtrahend.11_{2} minuend+10_{2 }R’s complement101 DifferenceDisregard the most significant 1, and the difference between 11_{2} and 10_{2} is 01_{2}. The most significant1 will not be used in the example shown in the following paragraph.

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