RFM42 Datasheet, PDF (22/110 Pages) –

RFM42/43
3.6.5. Frequency Offset Adjustment
A frequency offset can be adjusted manually by fo[9:0] in registers 73h and 74h. The frequency offset adjustment is
implemented by shifting the Synthesizer Local Oscillator frequency. This register is a signed register so in order to get
a negative offset you will need to take the twos complement of the positive offset number. The offset can be calculated
by the following:
DesiredOffset = 156.25Hz x (hbsel + 1) x fo[9 : 0]
DesiredOffset
fo[9 : 0] = _{156.25Hz x (hbsel + 1)}
The adjustment range in high band is: ±160 kHz, and adjustment range in low band is: ±80 kHz. For example to
compute an offset of +50 kHz in high band mode fo[9:0] should be set to 0A0h. For an offset of –50 kHz in high band
mode the fo[9:0] register should be set to 360h.
Function/Descri
Add R/W
D7 D6 D5
ption
D4 D3 D2 D1
Notes
D0 POR Def.
73 R/W Frequency Offset fo[7] fo[6] fo[5] fo[4] fo[3] fo[2] fo[1] fo[1]
00h
73
74 R/W Frequency Offset
fo[9] fo[8]
43h
3.6.6. TX Data Rate Generator
The data rate is configurable between 1–128 kbps. For data rates below 30 kbps the‖txdtrtscale‖ bit in register
70hshould be set to 1. When higher data rates are used this bit should be set to 0.
The TX date rate is determined by the following formula:
txdr[15:0] x1MHz
DR_ TX =
216+5*xdtrtscale
DR_ TX X 2 ^{16+5*xdtrtscale}
txdr[15:0] =
1MHz
The txdr register may be found in the following registers.
Add
6E
6F
R/W
R/W
R/W
Function/Des
cription
TX Data Rate 1
TX Data Rate 0
D7
txdr[15]
txdr[7]
D6
txdr[14]
txdr[6]
D5
txdr[13]
txdr[5]
D4
txdr[12]
txdr[4]
D3
txdr[11]
txdr[3]
D2
txdr[10]
txdr[2]
D1
txdr[9]
txdr[1]
D0
txdr[8]
txdr[0]
POR Def.
0Ah
AAh
22
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