Digital Logic 4-bit Multiplier/Adder

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Discussion Overview

The discussion focuses on designing a circuit that can either add or multiply two 4-bit numbers based on a control input. The context includes homework-related queries about using multiplexers (muxes), full adder circuits, and logic gates, with considerations for handling both positive and negative numbers using two's complement representation.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes their progress in building a full adder and a multiplier but expresses confusion about how to implement the muxes for switching between addition and multiplication based on the control input.
  • Another participant suggests that the mux output represents the final result, indicating that multiple muxes may be needed to handle each bit of the inputs separately.
  • A request is made for clarification on how to use the mux to allow user selection between the adder and multiplier functions.
  • One participant reiterates the function of the multiplexer, emphasizing that it should select between inputs A and B for each bit based on the control bit.
  • There is a question about whether to use a 4:1 mux or a 2:1 mux for the implementation.
  • Some participants assert that addition and multiplication are the only operations to be included in the mux.

Areas of Agreement / Disagreement

Participants express differing views on the implementation details of the muxes, particularly regarding the number of muxes required and the type of mux to use. The discussion remains unresolved with multiple competing perspectives on how to proceed.

Contextual Notes

There are limitations regarding the clarity of how to connect the circuits together and the specific requirements for the mux implementation. The discussion does not resolve these uncertainties.

roinujo1
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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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