In addition to the many core features that add to low power consumption, peripheral improvements also have helped. In the C8051F9xx family, the voltage reference is on and stable in less than 2µs. In addition to that, the ADC is able to track the input during this time so that the complete conversion happens within the ADC conversion rate without the added latency of the turn on time. This feature helps to maximize the inactive mode of the system. Finally, autonomous peripherals are those that can operate without CPU intervention and when the CPU is asleep. The UARTs, SPI, SMBus and ADC are all examples of these. The ADC can do burst samples and accumulate them while the CPU is inactive since the clock is independent of the CPU clock. Typically an MCU has to either remain awake or wake up to get the samples and perform the averaging function.