RFM31B Datasheet, PDF (21/57 Pages) List of Unclassifed Manufacturers – ISM RECEIVER

RFM31B
3.5.2. Easy Frequency Programming for FHSS
While Registers 73h–77h may be used to program the carrier frequency of the RFM31B,it is often easier to think in
terms of “channels” or “channel numbers” rather than an absolute frequency value in Hz. Also, there may be some
timing-critical applications (such as for Frequency Hopping Systems) in which it is desirable to change frequency
by programming a single register. Once the channel step size is set, the frequency may be changed by a single
register corresponding to the channel number. A nominal frequency is first set using Registers 73h–77h, as
described above. Registers 79h and 7Ah are then used to set a channel step size and channel number, relative to
the nominal setting. The Frequency Hopping Step Size (fhs[7:0]) is set in increments of 10 kHz with a maximum
channel step size of 2.56 MHz. The Frequency Hopping Channel Select Register then selects channels based on
multiples of the step size.
F_carrier  Fnom  fhs[7 : 0] ( fhch[7 : 0]10kHz)
For example, if the nominal frequency is set to 900 MHz using Registers 73h–77h, the channel step size is set to
1 MHz using "Register 7Ah. Frequency Hopping Step Size," and "Register 79h. Frequency Hopping Channel
Select" is set to 5d, the resulting carrier frequency would be 905 MHz. Once the nominal frequency and channel
step size are programmed in the registers, it is only necessary to program the fhch[7:0] register in order to change
the frequency.
Add R/W Function/Description
D7
D6
D5
D4
D3
D2
D1
D0 POR Def.
79 R/W Frequency Hopping Channel fhch[7] fhch[6] fhch[5] fhch[4] fhch[3] fhch[2] fhch[1] fhch[0] 00h
Select
7A R/W Frequency Hopping Step fhs[7] fhs[6] fhs[5] fhs[4] fhs[3] fhs[2] fhs[1] fhs[0] 00h
Size
3.5.3. Automatic State Transition for Frequency Change
If registers 79h or 7Ah are changed in RX mode, the state machine will automatically transition the chip back to
TUNE and change the frequency. This feature is useful to reduce the number of SPI commands required in a
Frequency Hopping System. This in turn reduces microcontroller activity, reducing current consumption.
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