System OFF is the deepest internal power saving mode the system can enter.
In this mode, the core system functionality is powered down and ongoing tasks terminated, and only the reset and the wakeup functions are available and responsive.
The device is put into System OFF mode using the REGULATORS register interface. When in System OFF mode, one of the following signals/actions will wake up the device:
When the device wakes up from System OFF mode, a system reset is performed.
One or more RAM blocks can be retained in System OFF mode depending on the settings in the RAM[n].POWER registers in VMC. RAM[n].POWER are retained registers, see Reset behavior. Note that these registers are usually overwritten by the startup code provided with the nRF application examples.
Before entering System OFF mode, the user must make sure that all on-going EasyDMA transactions have completed. This can be accomplished by making sure that EasyDMA enabled peripherals have stopped and END events from them received. The LTE modem also needs to be stopped, by issuing a command through the modem API, before entering System OFF mode. Once the command is issued, one should wait for the modem to respond that it actually has stopped, as there may be a delay until modem is disconnected from the network.