RFM95 Datasheet, PDF (77/121 Pages) List of Unclassifed Manufacturers – Low Power Long Range Transceiver Module

WIRELESS & SENSING
RFM95/96/97/98(W)
PRELIMINARY
DATASHEET
5.3.2. CLKOUT Output
The reference frequency, or a fraction of it, can be provided on DIO5 (pin 13) by modifying bits ClkOut in RegDioMapping2.
Two typical applications of the CLKOUT output include:
Š To provide a clock output for a companion processor, thus saving the cost of an additional oscillator. CLKOUT can be
made available in any operation mode except Sleep mode and is automatically enabled at power on reset.
Š To provide an oscillator reference output. Measurement of the CLKOUT signal enables simple software trimming of the
initial crystal tolerance.
Note To minimize the current consumption of the RFM95/96/97/98(W), please ensure that the CLKOUT signal is
disabled when not required.
5.3.3. PLL
The local oscillator of the RFM95/96/97/98(W) is derived from two almost identical fractional-N PLLs that are referenced
to the crystal oscillator circuit. Both PLLs feature a programmable bandwidth setting where one of four discrete preset
bandwidths may be accessed.
The RFM95/96/97/98(W) PLL uses a 19-bit sigma-delta modulator whose frequency resolution, constant over the whole
frequency range, is given by:
F_STEP =
-^F---^X---^O----^S---^C--
2¹⁹
The carrier frequency is programmed through RegFrf, split across addresses 0x06 to 0x08:
F_RF = F_STEP × Frf(23,0)
Note
The Frf setting is split across 3 bytes. A change in the center frequency will only be taken into account when the
least significant byte FrfLsb in RegFrfLsb is written. This allows the potential for user generation of m-ary FSK at
very low bit rates. This is possible where frequency modulation is achieved by direct programming of the
programmed RF centre frequency. To enable this functionality set the FastHopOn bit of register RegPllHop.
5.3.4. RC Oscillator
All timing operations in the low-power Sleep state of the Top Level Sequencer rely on the accuracy of the internal low-
power RC oscillator. This oscillator is automatically calibrated at the device power-up not requiring any user input.
Tel: [phone] Fax: [phone] E-mail: [e-mail] http:/ / www.hoperf.com
Page 77