RFM22 Datasheet, PDF (30/150 Pages) –

RFM22
4.2. Modulation Data Source
The RFM22 may be configured to obtain its modulation data from one of three different sources: FIFO mode, Direct
Mode, and from a PN9 mode. Furthermore, in Direct Mode, the TX modulation data may be obtained from several
different input pins. These options are set through the dtmod[1:0] field in "Register 71h. Modulation Mode Control
2"..
Function/Descr
Add R/W
D7
D6
D5
D4
D3 D2
D1
iption
POR
D0
Def.
Modulation Mode
dtmod dtmod
71 R/W
trclk[1] trclk[0]
eninv fd[8] modtyp[1] modtyp[0] 23h
Control 2
[1]
[0]
modtyp[1:0]
00
01
10
11
Modulation Source
Direct Mode using TX_Data via GPIO pin (GPIO needs programming accordingly also)
Direct Mode using TX_Data via SDI pin (only when nSEL is high)
FIFO Mode
PN9 (internally generated)
4.3. FIFO Mode
In FIFO mode, the integrated FIFOs are used to transmit and receive the data. The FIFOs are accessed via
"Register 7Fh. FIFO Access" with burst read/write capability. The FIFOs may be configured specific to the
application packet size, etc. (see "6. Data Handling and Packet Handler" for further information). When in FIFO mode
the module will automatically exit the TX or RX State when either the ipksent or ipkvalid interrupt occurs. The module
will return to any of the other states based on the settings in "Register 07h. Operating Mode and Function Control 1".
For instance, if the module is put into TX mode and both the txon and pllon bits are set, the module will transmit all of
the contents of the FIFO and the ipksent interrupt will occur. When this event occurs the module will clear the txon bit
and return to pllon or Tune Mode. If no other bits are set in register 07h besides txon initially then the module will
return to the Idle state. In RX mode the rxon bit will only be cleared if ipkvalid occurs. A CRC, Header, or Sync error
will generate an interrupt and the microcontroller will need to decide on the next action.
4.4. Direct Mode
For legacy systems that have packet handling within an MCU or other baseband module, it may not be desirable to
use the FIFO. For this scenario, a Direct Mode is provided which bypasses the FIFOs entirely. In Direct Mode, the
TX modulation data is applied to an input pin of the module and processed in ―real time‖ (i.e., not stored in a register
for transmission at a later time). There are various configurations for choosing which pin is used for the TX Data.
Furthermore, an additional input pin is required for the TX Data Clock if GFSK modulation is desired (only the TX
Data input pin is required for FSK). Two options for the source of the TX Data are available in the dtmod[1:0] field,
and various configurations for the source of the TX Data Clock may be selected through the trclk[1:0] field.
trclk[1:0]
TX Data Clock Configuration
00
No TX Clock (only for FSK)
01
TX Data Clock is available via GPIO (GPIO needs programming accordingly as well)
10
TX Data Clock is available via SDO pin (only when nSEL is high)
11
TX Data Clock is available via the nIRQ pin
The eninv bit in Address 71h will invert the TX Data for testing purposes.
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