A pulse generator includes a pulse command register and a digital differential analyzer (DDA). The pulse command register includes a first register, a second register, and an adder. The first register receives and stores a pulse command from a CPU in an operating cycle. The second register receives and stores the pulse command shifted from the first register when the first register receives a second pulse command from the CPU in the operating cycle. The adder sums the pulse commands of the first register and the second register and the result is transmitted to the DDA. The DDA determines whether a pulse is to be generated after calculation according to the result from the adder of the pulse command register.