ELEC1710 Lecture Notes - Lecture 4: Addition, Negative Number, Subtraction
8 Oct 2018
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Two columns for adding binary digits: carry, sum, once the sum column overflows, the value gets (cid:494)carried(cid:495) to the carry column, the value of the lsb. The technical term for the two values being added are augend and addend. Adding two bits has four possible cases. When a carry is generated in one column: need to add three bits in the next column, one bit from each number plus the carry bit. Half adder ignores the carry column: performs addition of two bits. Adds three bits: a, b and carry-in (cin) Use xor to simplify logic equation if there is an alternation between the cout and in the truth table (they are opposite values) Can also use two half-adders to construct full-adder. Full adders can be combined into parallel adders that can add binary numbers with multiple bits i. e. 32-bit value.
