Monday 27 March 2017

digital logic - 4-bit adder carry confusion


I try to design a circuit that adds two 4-bit binary numbers, but I get confused about the carry thingy.


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Above I add 0100 + 0101. The result should be 1001, but it shows 1100. buzzer


Later I did the 0110 + 1001 and it got it right (1111).


Then I tried 0111 + 0010 and I got 11010. buzzer


Is it the Half Adder fault?


Did I falsely connect each carry to the "CIN"s?



What's wrong?



Answer



Your switches are arranged LSb to MSb, but you're inputting the numbers MSb to LSb. Your schematic shows 0b0010 + 0b1010, with a correct result of 0b1100.


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