The ATSAMD21G18A-AU is a series of low-power Microcontroller Unit using the 32-bit ARM® Cortex®-M0+ processor and ranging from 32 to 64-pins with up to 256kB flash and 32kB of SRAM. It is designed for simple and intuitive migration with identical peripheral modules, hex compatible code, identical linear address map and pin compatible migration paths between all devices in the product series. All devices include intelligent and flexible peripherals, Atmel Event System for inter-peripheral signalling and support for capacitive touch button, slider and wheel user interfaces. All devices have accurate and low-power external and internal oscillators. All oscillators can be used as a source for the system clock. Different clock domains can be independently configured to run at different frequencies, enabling power saving by running each peripheral at its optimal clock frequency and thus maintaining a high CPU frequency while reducing power consumption.