RFM23
It is advised to disable the invalid preamble interrupt when Antenna Diversity is enabled. The Invalid Preamble
Detect interrupt may be triggered during the Antenna Diversity algorithm if one of the antennas is weak but the
other is capable of still receiving the signal if the Antenna Diversity algorithm is allowed to complete.
6.9. TX Retransmission and Auto TX
The RFM23 is capable of automatically retransmitting the last packet in the FIFO if no additional packets were loaded into the TX
FIFO. Automatic Retransmission is achieved by entering the TX state with the txon bit set. This feature is useful for Beacon
transmission or when retransmission is required due to the absence of a valid acknowledgement. Only packets that fit completely
in the TX FIFO are valid for retransmit. When it is necessary to transmit longer packets, the TX FIFO uses the circular read/write
capability.
An Automatic Transmission is also available. When autotx = 1 the transceiver will enter automatically TX State when the TX FIFO
is almost full. When the packet is sent, the transceiver will automatically return to the IDLE State.
POR
D7
D6
D5
D4
D3
D2
D1
D0
Add R/W Function/Description
Def.
Operating &Function
R/W
Reserved
autotx
Reserved
Reserved
ffclrtx
00h
08
Control 2
7. RX Modem Configuration
7.1. Modem Settings for FSK and GFSK
The modem performs channel selection and demodulation in the digital domain. The channel filter bandwidth is
configurable from 620 to 2.6 kHz. The data-rate, modulation index, and bandwidth are set via registers 1C–25. The
modulation index is equal to 2 times the peak deviation divided by the data rate (Rb).
Table 16 gives the modem register settings for various common data-rates. Select the desired data-rate (Rb), and
Deviation (Fd) to determine the proper register settings. For data-rates and modulation types not listed in the table
a calculator tool within EXCEL can be used.
When Manchester coding is disabled, the required channel filter bandwidth is calculated as BW = 2 x (Fd + 0.25Rb)
where Fd is the frequency deviation and Rb is the data rate. For modulation indices below 1 the required channel
filter bandwidth is calculated as BW = Fd + Rb. The channel filter needs to be increased when the frequency offset
between transmitter and receiver is more than half the channel filter bandwidth. In this case it is recommended to
enable the AFC and choose the IF bandwidth equal to 2 x frequency offset.
Table 16. RX Modem Configurations for FSK and GFSK
RX Modem setting examples for GFSK and FSK
Application parameters
Register values (hex)
Rb
kbps
2
Fd
kHz
5
mod index
BW -3dB
kHz
dwn3_bypass
ndec_exp[2:0]
filset[3:0]
rxosr[10:0] ncoff[19:0] crgain[10:0]
1Ch
0
1Ch
3
1Ch
3
20,21h
0FA
0D0
683
21,22,23h
08312
09D49
013A9
13A93
02752
13A93
04EA5
147AE
24,25h
06B
0A0
005
5.00
4.00
30.00
2.00
18.75
1.00
9.38
1.00
11.5
11.5
75.2
12.1
95.3
18.9
95.3
18.9
2.4
2.4
4.8
4.8
9.6
9.6
10
4.8
36
4.8
45
4.8
45
5
0
3
3
0
0
1
0
3
4
068
278
0
0
4
341
00A
4EE
024
0
2
1
068
0
0
4
1A1
064
0
2
1
521
44
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