Manual

RF22
Version: 0.1 Date: 12/23/2008
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14
Table12. Frequency Band Selection
Frequency Band
fb[4:0] Value N
hbsel=0 hbsel=1
0 24 240-249.9MHz 480-489.9MHz
1 25 250-259.9MHz 500-509.9MHz
2 26 260-269.9MHz 520-529.9MHz
3 27 270-279.9MHz 540-549.9MHz
4 28 280-289.9MHz 560-569.9MHz
5 29 290-299.9MHz 580-589.9MHz
6 30 300-309.9MHz 600-609.9MHz
7 31 310-319.9MHz 620-629.9MHz
8 32 320-329.9MHz 640-649.9MHz
9 33 330-339.9MHz 660-669.9MHz
10 34 340-349.9MHz 680-689.9MHz
11 35 350-359.9MHz 700-709.9MHz
12 36 360-369.9MHz 720-729.9MHz
13 37 370-379.9MHz 740-749.9MHz
14 38 380-389.9MHz 760-769.9MHz
15 39 390-399.9MHz 780-789.9MHz
16 40 400-409.9MHz 800-809.9MHz
17 41 410-419.9MHz 820-829.9MHz
18 42 420-429.9MHz 840-849.9MHz
19 43 430-439.9MHz 860-869.9MHz
20 44 440-449.9MHz 880-889.9MHz
21 45 450-459.9MHz 900-909.9MHz
22 46 460-469.9MHz 920-930MHz
23 47 470-479.9MHz 
The chip will automatically shift the frequency of the Synthesizer down by 937.5 kHz (30 MHz ÷ 32) to achieve the
correct Intermediate Frequency (IF) when RX mode is entered. Low-side injection is used in the RX Mixing architecture;
therefore, no frequency reprogramming is required when using the same TX frequency and switching between RX/TX
modes.
3.2.9.2. Easy Frequency Programming for FHSS
While Registers 73h–77h may be used to program the carrier frequency of the RF22, 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.
[
]
[
]
(
)
kHzfhchfhsFnomf
TX
100:70:7
×
×
+
=
For example: if the nominal frequency is set to 900 MHz using Registers 73h–77h and the channel step size is set to 1
MHz using "Register 7Ah. Frequency Hopping Step Size". For example, if the "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 Select
fhch[7] fhch[6] fhch[5] fhch[4] fhch[3] fhch[2] fhch[1] fhch[0] 00h
7A R/W Frequency Hopping
Step Size
fhs[7] fhs[6] fhs[5] fhs[4] fhs[3] fhs[2] fhs[1] fhs[0] 00h