The proper way of changing the system clock when both the clock source and the clock divide value are being changed is as follows: If switching from a fast “undivided” clock to a slower “undivided” clock: 1. Change the clock divide value. 2. Poll for CLKRDY > 1. 3. Change the clock source. If switching from a slow “undivided” clock to a faster “undivided” clock: 1. Change the clock source. 2. Change the clock divide value. 3. Poll for CLKRDY > 1.