Reset

A system reset can be triggered by multiple sources. After a reset the CPU can query the RESETREAS (reset reason register) to find out which source generated the reset.

Power-on reset

The power-on reset generator initializes the system at power-on. The system is held in reset state until the supply has reached the minimum operating voltage and the internal voltage regulators have started.

Pin reset

A pin reset is generated when the physical reset pin (nRESET) on the device is pulled low.

To ensure that reset is issued correctly, the reset pin should be held low for the time specified in Pin reset.

nRESET pin has an always-on internal pull-up resistor connected to nRF9160 internal voltage typically of 2.2 V level, as illustrated in the following figure. The value of the pull-up resistor is given in Pin reset.

Note: Driving nRESET high with a voltage lower than 2.2V will result in additional leakage.
Figure 1. Pin reset internal generation


Wakeup from System OFF mode reset

The device is reset when it wakes up from System OFF mode.

The Debug access port is not reset following a wake up from System OFF mode if the device is in debug interface mode, see Debug and trace chapter for more information.

Soft reset

A soft reset is generated when the SYSRESETREQ bit of the application interrupt and reset control register (AIRCR register) in the Arm® core is set.

Watchdog reset

A watchdog reset is generated when the watchdog timer (WDT) times out.

See WDT — Watchdog timer chapter for more information.

Brownout reset

The brownout reset generator puts the system in reset state if the supply voltage drops below the brownout reset threshold.

Retained registers

A retained register is a register that will retain its value in System OFF mode, and through a reset depending on reset source. For information on which peripheral registers are retained, see the corresponding peripheral's chapter.

Reset behavior

Reset behavior depends on the reset source.

The reset behavior is summarized in the table below.

Table 1. Reset behavior for the main components
Reset sourceReset target
CPUModemDebug1SWJ-DPNot retained RAM2Retained RAM2WDTRESETREAS
CPU lockup 3xx
Soft resetxx
Wakeup from System OFF mode resetxxx 4xx
Watchdog reset 5xxxxxx
Pin resetxxxxxxx
Brownout resetxxxxxxxx
Power-on resetxxxxxxx
Note: The RAM is never reset but its content might be corrupted after reset in the cases given in the table above.
Table 2. Reset behavior for the retained registers
Reset sourceReset target
Regular peripheral registersGPIO, SPUNVMC WAITSTATENUMNVMC IFCREADDELAYREGULATORS, OSCILLATORSPOWER.GPREGRET
CPU lockup3xxx
Soft resetxxx
Wakeup from System OFF mode resetxx
Watchdog reset5xxxx
Pin resetxxxx
Brownout resetxxxxxx
Power-on resetxxxxxx

Electrical specification

Pin reset

SymbolDescriptionMin.Typ.Max.Units
tHOLDRESET

Hold time for reset pin when doing a pin reset

5µs
RPULL-UP

Value of the internal pull-up resistor

13kΩ
1 All debug components excluding SWJ-DP. See Debug and trace chapter for more information about the different debug components in the system.
2 RAM can be configured to be retained using registers in VMC — Volatile memory controller
3 Reset from CPU lockup is disabled if the device is in debug interface mode. CPU lockup is not possible in System OFF.
4 The debug components will not be reset if the device is in debug interface mode.
5 Watchdog reset is not available in System OFF.