RFM42 Datasheet, PDF (24/110 Pages) –

RFM42/43
4.2. Modulation Data Source
The RFM42/43 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]
Modulation Source
00
Direct Mode using TX_Data via GPIO pin (GPIO needs programming accordingly also)
01
Direct Mode using TX_Data via SDI pin (only when nSEL is high)
10
FIFO Mode
11
PN9 (internally generated)
4.3. FIFO Mode
In FIFO mode, the integrated FIFO is used to transmit the data. The FIFO is accessed via "Register 7Fh. FIFO
Access" with burst write capability. The FIFO 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 State when the ipksent 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 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.
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]
00
01
10
11
TX Data Clock Configuration
No TX Clock (only for FSK)
TX Data Clock is available via GPIO (GPIO needs programming accordingly as well)
TX Data Clock is available via SDO pin (only when nSEL is high)
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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