RFM22
3.2.3. TX State
The TX state may be entered from any of the IDLE modes when the txon 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 between
states from enabling the crystal oscillator to ramping up the PA to prevent unwanted spectral splatter. The following
sequence of events will occur automatically when going from STANDBY mode to TX mode by setting the txon bit.
1. Enable the Main Digital LDO and the Analog LDOs.
2. Start up crystal oscillator and wait until ready (controlled by timer).
3. Enable PLL.
4. Calibrate VCO (this action is skipped when the vcocal bit is ―0‖, default value is ―1‖).
5. Wait until PLL settles to required transmit frequency (controlled by timer).
6. Activate Power Amplifier and wait until power ramping is completed (controlled by timer).
7. Transmit Packet.
The first few steps may be eliminated depending on which IDLE mode the module is configured to prior to setting the
txon bit. By default, the VCO and PLL are calibrated every time the PLL is enabled. If the ambient temperature is
constant and the same frequency band is being used these functions may be skipped by setting the appropriate
bits in "Register 55h. Calibration Control".
3.2.4. 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:
1. Enable the Main Digital LDO and the Analog LDOs.
2. Start up crystal oscillator and wait until ready (controlled by timer).
3. Enable PLL.
4. Calibrate VCO (this action is skipped when the vcocal bit is ―0‖, default value is ―1‖).
5. Wait until PLL settles to required transmit frequency (controlled by timer).
6. Enable receive circuits: LNA, mixers, and ADC.
7. Calibrate ADC (RC calibration).
8. Enable receive mode in the digital modem.
Depending on the configuration of the radio all or some of the following functions will be performed automatically by
the digital modem: AGC, AFC (optional), update status registers, bit synchronization, packet handling (optional)
including sync word, header check, and CRC.
3.2.5. Device Status
D7
D6
D5
D4
D3
D2
D1
D0
POR Def.
Add R/W Function/Description
02 Device Status
R
ffovfl ffunfl rxffem
headerr freqerr lockdet
cps[1]
cps[0]
—
The operational status of the module can be read from "Register 02h. Device Status".
18
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