Capacitance is represented as a function of time (RC time constant) which can be measured with a timer peripheral on the MSP430. The designer has a choice between the RC or the RO method. Both methods are based upon the RC time constant created by the capacitive element and some internal or external resistance. With the RC method, the measurement window is the rise and fall time, and the timer counts the number of clocks (typically SMCLK cycles) within that measurement window. As the capacitance increases the time constant increases and consequently the measurement window increases. This is represented by an increase in the number of counts. With the RO method, a feedback loop uses the charge and discharge to create a relaxation oscillator. The frequency of the oscillation is a function of the capacitance. The measurement window is now a fixed time and the number of counts within that measurement window represents the frequency of the relaxation oscillator.