RFM22
POR
Def.
Function/Descri
ption
D7
D6
D5
D4
D3
D2
D1
D0
Add R/W
Operating &Function
Control 2
antdi
v[2]
antdi
v[1]
antdiv[
0]
R/W
00h
37h
04h
rxmpk
autotx
enldm
ffclrrx
ffclrtx
08
R/W
TX FIFO Control 1
txafthr[5] txafthr[4] txafthr[3] txafthr[2]
txaethr[ txaethr[ txaethr[ txaethr[
txafthr[1]
txaethr[
1]
txafthr[0]
txaethr[
0]
7C
R/W
TX FIFO Control 2
7D
5]
4]
3]
2]
The RX FIFO has one programmable threshold called the FIFO Almost Full Threshold, rxafthr[5:0]. When the
incoming RX data reaches the Almost Full Threshold an interrupt will be generated to the microcontroller via the
nIRQ pin. The microcontroller will then need to read the data from the RX FIFO.
POR
Function/D
escription
RX FIFO
D7
D6
D5
D4
D3
D2
D1
D0
Add R/W
Def.
rxafthr rxafthr rxafthr rxafthr
[3] [2] [1] [0]
R/W
Reserved Reserved rxafthr[5] rxafthr[4]
37h
7E
Control
Both the TX and RX FIFOs may be cleared or reset with the ffclrtx and ffclrrx bits in ―Register 08h. Operating Mode
and Function Control 2,‖. All interrupts may be enabled by setting the Interrupt Enabled bits in "Register 05h.
Interrupt Enable 1" and ―Register 06h. Interrupt Enable 2,‖. If the interrupts are not enabled the function will not
generate an interrupt on the nIRQ pin but the bits will still be read correctly in the Interrupt Status registers.
6.2. Packet Configuration
When using the FIFOs, automatic packet handling may be enabled for TX mode, RX mode, or both. "Register 30h.
Data Access Control" through ―Register 4Bh. Received Packet Length,‖ control the configuration,status, and
decoded RX packet data for Packet Handling. The usual fields for network communication (such as preamble,
synchronization word, headers, packet length, and CRC) can be configured to be automatically added to
the data payload. The fields needed for packet generation normally change infrequently and can therefore be
stored in registers. Automatically adding these fields to the data payload greatly reduces the amount of
communication between the microcontroller and the RFM22 and therefore also reduces the required computational
power of the microcontroller.
The general packet structure is shown in Figure 17. The length of each field is shown below the field. The preamble
pattern is always a series of alternating ones and zeroes, starting with a one. All the fields have programmable
lengths to accommodate different applications. The most common CRC polynominals are available for selection.
Figure 17. Packet Structure
An overview of the packet handler configuration registers is shown in Table 14. A complete register description can
be found in ―12.1. Complete Register Table and Descriptions‖.
38
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