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How do adders work? (AQA)
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tShephard
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I'm revising Logic Gates for computer science, currently on the adders part, but I cant work out how the addition works. I understand the half adder addition (0+0 = 0, 0+1 = 1, 1+1 = 1 carry 1), that all makes sense to me, but with full adders, looking at the truth table I don't understand it. What I mean is like 1 + 1 + 0 should, by half adder logic, equal 1 carry 1 (because + 0 doesn't add anything, right?) , but in reality it's 0 carry 1. very confused. if someone could explain how it works i'd be very thankful
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Hoc est Bellum
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#2
(Original post by tShephard)
I'm revising Logic Gates for computer science, currently on the adders part, but I cant work out how the addition works. I understand the half adder addition (0+0 = 0, 0+1 = 1, 1+1 = 1 carry 1), that all makes sense to me, but with full adders, looking at the truth table I don't understand it. What I mean is like 1 + 1 + 0 should, by half adder logic, equal 1 carry 1 (because + 0 doesn't add anything, right?) , but in reality it's 0 carry 1. very confused. if someone could explain how it works i'd be very thankful
I'm revising Logic Gates for computer science, currently on the adders part, but I cant work out how the addition works. I understand the half adder addition (0+0 = 0, 0+1 = 1, 1+1 = 1 carry 1), that all makes sense to me, but with full adders, looking at the truth table I don't understand it. What I mean is like 1 + 1 + 0 should, by half adder logic, equal 1 carry 1 (because + 0 doesn't add anything, right?) , but in reality it's 0 carry 1. very confused. if someone could explain how it works i'd be very thankful
So 1+1 in a half adder is the same as 1+1+0 in a full adder (=0 carry 1).
1+1 = 2
1+1+0 = 2
Both the operations have the same result and therefore the same output (0 carry 1)
The only real difference is that you can have the extra operation 1+1+1 = 1 carry 1.
I think you've looked at it wrong, you said that 1+1+0 should equal 1 by half adder logic, but by half adder logic 1+1+0 would still equal 0 carry 1 because 1+1+0 is the same as 1+1
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tShephard
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#3
(Original post by Hoc est Bellum)
I think you've looked at it wrong, you said that 1+1+0 should equal 1 by half adder logic, but by half adder logic 1+1+0 would still equal 0 carry 1 because 1+1+0 is the same as 1+1
I think you've looked at it wrong, you said that 1+1+0 should equal 1 by half adder logic, but by half adder logic 1+1+0 would still equal 0 carry 1 because 1+1+0 is the same as 1+1
Is it just straight up wrong or is there something im missing?
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Hoc est Bellum
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#4
(Original post by tShephard)
I said that because the notes on mathsandphysicstutor.com show this
Is it just straight up wrong or is there something im missing?
I said that because the notes on mathsandphysicstutor.com show this
Is it just straight up wrong or is there something im missing?
If the answer is 0, it is 0 carry 0
If the answer is 1, it is 1 carry 0
If the answer is 2, it is 0 carry 1
If the answer is 3, it is 1 carry 1
This is the same for both half and full adders
For example
1+1+0 = 2 so it is 0 carry 1
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tShephard
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#5
(Original post by Hoc est Bellum)
Just think about it this way
If the answer is 0, it is 0 carry 0
If the answer is 1, it is 1 carry 0
If the answer is 2, it is 0 carry 1
If the answer is 3, it is 1 carry 1
This is the same for both half and full adders
For example
1+1+0 = 2 so it is 0 carry 1
Just think about it this way
If the answer is 0, it is 0 carry 0
If the answer is 1, it is 1 carry 0
If the answer is 2, it is 0 carry 1
If the answer is 3, it is 1 carry 1
This is the same for both half and full adders
For example
1+1+0 = 2 so it is 0 carry 1
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DFranklin
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#6
(Original post by tShephard)
I'm revising Logic Gates for computer science, currently on the adders part, but I cant work out how the addition works. I understand the half adder addition (0+0 = 0, 0+1 = 1, 1+1 = 1 carry 1),
I'm revising Logic Gates for computer science, currently on the adders part, but I cant work out how the addition works. I understand the half adder addition (0+0 = 0, 0+1 = 1, 1+1 = 1 carry 1),
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