Adder/Subtractor

Using four of your full adder components (described above), in a separate circuit (called ADD_SUB) create a 4-bit adder/subtractor component. The circuit will take two sets of 4-bit inputs (A3-A0 and B3-B0), plus two additional inputs SUB (if true, SUBTRACT, otherwise ADD) and ENABLE (if true, all outputs are enabled using tri-state buffers, if false, all outputs are disabled). The circuit will produce a 4-bit sum (S3-S0) or difference (when subtracting).

The basic circuit is given below (without the ENABLE input). In this circuit, the K input is the same as our SUB input.

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