RFM31
3.2.1. Shutdown State
The shutdown state is the lowest current consumption state of the device with nominally less than 10 nA of current consumption.
The shutdown state may be entered by driving the SDN pin high. The SDN pin should be held low in all states except the
SHUTDOWN state. In the SHUTDOWN state, the contents of the registers are lost and there is no SPI access.
When the module is connected to the power supply, a POR will be initiated after the falling edge of SDN.
3.2.2. Idle State
There are four different modes in the IDLE state which may be selected by "Register 07h. Operating Mode and Function Control
1". All modes have a tradeoff between current consumption and response time to RX mode. This tradeoff is shown in Table 10.
After the POR event, SWRESET, or exiting from the SHUTDOWN state the module will default to the IDLE-READY mode. After a
POR event the interrupt registers must be read to properly enter the SLEEP, SENSOR, or STANDBY mode and to control the 32
kHz clock correctly.
3.2.2.1. STANDBY Mode
STANDBY mode has the lowest current consumption possible with only the LPLDO enabled to maintain the register values. In
this mode the registers can be accessed in both read and write mode. The standby mode can be entered by writing 0h to Register
07h. Operating Mode and Function Control 1". If an interrupt has occurred (i.e., the nIRQ pin = 0) the interrupt registers must be
read to achieve the minimum current consumption. Additionally, the ADC should not be selected as an input to the GPIO in this
mode as it will cause excess current consumption.
3.2.2.2. SLEEP Mode
In SLEEP mode the LPLDO is enabled along with the Wake-Up-Timer, which can be used to accurately wake-up the radio at
specified intervals. See "8.6. Wake-Up Timer" for more information on the Wake-Up-Timer. Sleep mode is entered by setting enwt
= 1 (40h) in "Register 07h. Operating Mode and Function Control 1". If an interrupt has occurred (i.e., the nIRQ pin = 0) the
interrupt registers must be read to achieve the minimum current consumption. Also, the ADC should not be selected as an input to
the GPIO in this mode as it will cause excess current consumption.
3.2.2.3. SENSOR Mode
In SENSOR Mode either the Low Battery Detector, Temperature Sensor, or both may be enabled in addition to the LPLDO and
Wake-Up-Timer. The Low Battery Detector can be enabled by setting enlbd = 1 and the temperature sensor can be enabled by
setting ents = 1 in "Register 07h. Operating Mode and Function Control 1". See "8.4.Temperature Sensor" and "8.5. Low Battery
Detector" for more information on these features. If an interrupt has occurred (i.e., the nIRQ pin = 0) the interrupt registers must be
read to achieve the minimum current consumption.
3.2.2.4. READY Mode
READY Mode is designed to give a fast transition time to RX mode with reasonable current consumption. In this mode the Crystal
oscillator remains enabled reducing the time required to switch to the RX mode by eliminating the crystal start-up time. Ready
mode is entered by setting xton = 1 in "Register 07h. Operating Mode and Function Control 1". To achieve the lowest current
consumption state the crystal oscillator buffer should be disabled. This is done by setting "Register 62h. Crystal
Oscillator/Power-on-Reset Control" to a value of 02h. To exit ready mode, bufovr (bit 1) of this register must be set back to 0.
3.2.2.5. TUNE Mode
In TUNE Mode the PLL remains enabled in addition to the other blocks enabled in the IDLE modes. This will give the fastest
response to RX mode as the PLL will remain locked but it results in the highest current consumption. This mode of operation is
designed for Frequency Hopping Systems (FHS). Tune mode is entered by setting pllon = 1 in "Register 07h. Operating Mode and
Function Control 1". It is not necessary to set xton to 1 for this mode, theinternal state machine automatically enables the crystal
oscillator.
3.2.3. RX State
The RX state may be entered from any of the Idle modes when the rxon bit is set to 1 in "Register 07h. Operating Mode and
Function Control 1". A built-in sequencer takes care of all the actions required to transition from one of the IDLE modes to the RX
state. The following sequence of events will occur automatically to get the module into RX mode when going from STANDBY
mode to RX mode by setting the rxon bit:
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