Let’s look at an example of setting up the PLL. Let’s assume that the source is a 4MHz crystal. We would like to run our device at 30MIPS. So, how to set up the PLL. First, we need to select a pre-scalar value. Since our source clock is relatively low frequency, let’s use the minimal divisor of two. This results in 2MHz into the phase comparator, which is within the 0.8 to 8MHz specified range, so this is OK.