* The most significant carry bit is ignored. The logic is simple here, we simpley consume two 16 bits and output the sum of them: We will build a 16 bit Adder in this chapter. The chip whose job is to add such numbers is called a multi- bit adder, or simply adder.

Memory and register chips represent integer numbers by n-bit patterns, n being 16, 32, 64, and so forth-depending on the computer platform. Like the half-adder case, the full-adder chip produces two outputs: the least significant bit of the addition and the carry bit.įourOr(a=and1,b=and2,c=and3,d=and4,out=sum) įourOr(a=and5,b=and6,c=and7,d=and8,out=carry) Now that we know how to add two bits, we also need to design a chip to add three bits. It's not diffcult for us to write down its boolean expression since we have known its truth table:Ĭarry = a*b, sum = !a*b + a*!b, pretty easy, right? Half AdderĪs we can see, 'Half Adder' consumes two input bits and outputs one a bit and a sum bit. We will build four chips in this chapter: In this chapter we build gate logic designs that represent numbers and perform arithmetic operations on them. Counting is the religion of this generation, its hope and salvation - Gertrude Stein

2 bit half adder truth table