The Flash Write (FLWR) mode of the Flash controller enables writes to the Flash array to start a programming operation. Several writes can be done while the FLWR mode is enabled in the NVMCTRL.CTRLA register. When the FLWR mode is enabled, the ST* instructions write one byte at a time, while the SPM instruction writes one word at a time.
Before a write is performed to an address, its content needs to be erased.