Specifications

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RFM97C
B
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Applications
Crystal Resonator Specification
Table 43 shows the crystal resonator specification for the crystal reference oscillator circuit of the RFM97C(W).
This specification covers the full range of operation of the RFM97C(W) and is employed in the reference design.
Symbol Description Conditions Min Typ Max Unit
FXOSC XTAL Frequency - 32 - MHz
RS XTAL Serial Resistance - 30 TBC ohms
C0 XTAL Shunt Capacitance - 2.8 TBC pF
CFOOT External Foot Capacitance On each pin XTA and XTB 8 15 22 pF
CLOAD
Notes - the initial frequency tolerance, temperature stability and ageing performance should be chosen in accordance
with the target operating temperature range and the receiver bandwidth selected.
- the loading capacitance should be applied externally, and adapted to the actual Cload specification of the XTAL.
Receiver Restart Methods
The options for restart of the receiver are covered below. This is typically of use to prepare for the reception of a new signal
whose strength or carrier frequency is different from the preceding packet to allow the AGC or AFC to be re-evaluated.
Restart Upon User Request
In Receive mode the user can request a receiver restart - this can be useful in conjunction with the use of a Timeout
interrupt following a period of inactivity in the channel of interest. Two options are available:
 No change in the Local Oscillator upon restart: the AFC is disabled, and the Frf register has not been changed through
SPI before the restart instruction: set bit RestartRxWithoutPllLock in RegRxConfig to 1.
 Local Oscillator change upon restart: if AFC is enabled (AfcAutoOn=1), and/or the Frf register had been changed during
the last Rx period: set bit RestartRxWithPllLock in RegRxConfig to 1.
Note ModeReady must be at logic level 1 for a new RestartRx command to be taken into account.
Automatic Restart after valid Packet Reception
The bits AutoRestartRxMode in RegSyncConfig control the automatic restart feature of the RFM97C(W) receiver, when a
valid packet has been received:
 If AutoRestartRxMode = 00, the function is off, and the user should manually restart the receiver upon valid packet
reception
 If AutoRestartRxMode = 01, after the user has emptied the FIFO following a PayloadReady interrupt, the receiver will
automatically restart itself after a delay of InterPacketRxDelay, allowing for the distant transmitter to ramp down, hence
avoiding a false RSSI detection on the ‘tail’ of the previous packet.
 If AutoRestartRxMode = 10 should be used if the next reception is expected on a new frequency, i.e. Frf is changed
after the reception of the previous packet. An additional delay is systematically added, in order for the PLL to lock at a
new frequency.