Digital Logic 4-bit Multiplier/Adder

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The discussion focuses on designing a circuit that can either add or multiply two 4-bit numbers based on a control input, using two's complement for positive and negative numbers. Participants clarify the use of multiplexers (muxes) to switch between the addition and multiplication outputs, emphasizing that one mux per bit is necessary to handle the control input effectively. There is confusion about whether to use 4:1 or 2:1 muxes, with the consensus leaning towards 2:1 since only two operations are involved. The final output from the mux will depend on the control input, determining whether the result is from the adder or the multiplier. Overall, the thread seeks to clarify the implementation of muxes in the circuit design.
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Homework Statement


Build a circuit that either adds or multiplies two 4-bit numbers based on a control input C(C is 1 add, C is zero multiply). Numbers are positive and negative so use two's complement. You can use muxes, Full Adder Circuits, and logic gates

Homework Equations


Multiplier circuit=
upload_2016-10-10_16-2-7.png


Adder Circuit:
upload_2016-10-10_16-10-34.png

The Attempt at a Solution


So, I have built both the Full Adder(for the addition part) and the multiplier. However, I don't know how to use the muxes to get the input switching if control is 0 and 1. Since the mux only has one output, I don't understand how to connect the two circuits together. Any help is much appreciated!
 
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The mux output is the final result - one bit of the addition or multiplication depending on the state of C. Where do you expect more outputs? You'll need one mux per bit (or a mux block that can handle multiple bits in parallel).
 
Can you please show how we can use the mux to let the user choose between adder or multiplayer ?
 
This thread is half a year old.
The multiplexer looks like every other multiplexer - for each bit, choose either input A or input B as output, depending on a control bit. Do that for all 4 bits.
 
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mfb said:
This thread is half a year old.
The multiplexer looks like every other multiplexer - for each bit, choose either input A or input B as output, depending on a control bit. Do that for all 4 bits.
should we use 4:1 mux or 2:1 mux ?
 
Addition and multiplication are 2 operations. What else do you want to put into the MUX?
 
mfb said:
Addition and multiplication are 2 operations. What else do you want to put into the MUX?
only addition and multiplication.
 

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