RFM22
Register 1Fh. Clock Recovery Gearshift Override
Bit
D7
Reserved
R/W
D6
rxready
R/W
D5
D4
D3
D2
D1
D0
crfast[2:0]
R/W
crslow[2:0]
R/W
Name
Type
Reset value = 00000011
Bit
Name
Function
Reserved
Reserved.
Improves Receiver Noise Immunity when in Direct Mode.
7
It is recommended to set this bit after preamble is detected. When in FIFO
mode this bit should be set to ―0‖ since noise immunity is controlled
automatically.
rxready
6
crfast[2:0]
crslow[2:0]
5:3
2:0
Clock Recovery Fast Gearshift Value.
Clock Recovery Slow Gearshift Value.
ndec_exp
The oversampling rate can be calculated as rxosr = 500 kHz/(2
x RX_DR). The ndec_exp and the
dwn3_bypass values found at Address: 1Ch – IF Filter Bandwidth register together with the receive data rate (Rb)
are the parameters needed to calculate rxosr:
500×(1+2×dwn3_bypass)
rxosr =
2
ndec_exp-3 ×Rb×（1+enmanch）
The Rb unit used in this equation is in kbps. The enmanch is the Manchester Coding parameter (see Reg. 70h,
enmach is 1 when Manchester coding is enabled, enmanch is 0 when disabled). The number found in the equation
should be rounded to an integer. The integer can be translated to a hexadecimal.
For optimal modem performance it is recommended to set the rxosr to at least 8. A higher rxosr can be obtained by
choosing a lower value for ndec_exp or enable dwn3_bypass. A correction in filset might be needed to correct the
channel select bandwidth to the desired value. Note that when ndec_exp or dwn3_bypass are changed the related
parameters (rxosr, ncoff and crgain) need to be updated.
97
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