The Dual Clock Comparator (DCC) module determines the accuracy of selectable clock sources by counting the pulses of two independent clock sources (counter 0 and counter 1). If one clock is out of spec, an error signal is generated. For example, the DCC1 can be configured to use CLK10M as the reference clock (for counter 0) and VCLK as the "clock under test" (for counter 1). This configuration allows the DCC1 to monitor the PLL output clock when VCLK is using the PLL output as its source.

An additional use of this module is to measure the frequency of a selectable clock source. For example, the reference clock is connected to Counter 0 and the signal to be measured is connected to Counter 1. Counter 0 is programmed with a start value of known time duration (measurement time) from the reference clock. Counter 1 is programmed with a maximum start value. Start both counter simultaneously. When Counter 0 decrements to zero, both counter will stop and an error signal is generated if Counter 1 does not reach zero. The frequency of the input signals can be calculated from the count value of Counter 1 and the measurement time.