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#1




4bit Parallel Adder > Subtractor
I just drew this up real quickly in Photoshop. So the objective is to use the IC and four inverters to create a subtractor circuit that'll do the following operation: A4 A3 A2 A1  B4 B3 B2 B1 So would I just invert all the B's on the circuit? 
#2




Connect the outputs of 4 XOR gates to B1B4. Connect one of each XOR's gate input to C1. The other four inputs on the XOR gates (one input per gate) are your new inputs for B1B4. When you apply high logic to Cin the circuit will subtract AB , when you apply low logic to Cin the circuit will add A+B.
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#3




Is there a way to just do it with inverters? The worksheet we were given only says "Use the IC below and 4 inverters to subtract..."
I was trying to figure out how on earth to do the 2's complement method with this, are using the XOR gates the only way? 
#4




Hint:
A  B = A + 2's complement of B 2's complement of B = B' + 1 
#5




Quote:
With this modification you invert all the bits and add 1 as the 2's complements requires. The circuit will do the function AB.
__________________
>> Troubleshooting is an art << http://www.youtube.com/watch?v=hC7KYbFBPHA http://www.youtube.com/watch?v=StNJlRTWs9k http://www.youtube.com/watch?v=j4h3l9O4fc http://www.youtube.com/watch?v=E0jZJ...eature=related 
#6




So the carryin high is basically the 1 that is added when a 2's complement is performed?
I believe I understand now, thanks a bunch to the both of you! Hopefully I'll be ready for the exam come tomorrow. 
#7




yes the carry in is the 1 we add n the 2's complement.
__________________
>> Troubleshooting is an art << http://www.youtube.com/watch?v=hC7KYbFBPHA http://www.youtube.com/watch?v=StNJlRTWs9k http://www.youtube.com/watch?v=j4h3l9O4fc http://www.youtube.com/watch?v=E0jZJ...eature=related 
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>, 4bit, adder, parallel, subtractor 
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