Data Sheet

Page 69
RFM95/96/97/98(W)
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WIRELESS & SENSING PRELIMINARY DATASHEET
 Optional 2-bytes CRC checksum
Optional DC free data coding
CRC checksum calculation
Preamble
0 to 65536 byte
s
Sync Word
0 to 8 bytes
Length
byte
Address
byte
Message
Up to 255 bytes
CRC
2-bytes
Payload
(min 2 bytes)
Fields added by the packet handler in Tx and processed and removed in Rx
Optional User provided fields which are part of the payload
Message part of the payload
Figure 34. Variable Length Packet Format
Unlimited Length Packet Format
Unlimited length packet format is selected when bit PacketFormat is set to 0 and PayloadLength is set to 0. The user can
then transmit and receive packet of arbitrary length and PayloadLength register is not used in Tx/Rx modes for counting
the length of the bytes transmitted/received.
In Tx the data is transmitted depending on the TxStartCondition bit. On the Rx side the data processing features like
Address filtering, Manchester encoding and data whitening are not available if the sync pattern length is set to zero
(SyncOn = 0). The filling of the FIFO in this case can be controlled by the bit FifoFillCondition. The CRC detection in Rx is
also not supported in this mode of the packet handler, however CRC generation in Tx is operational. The interrupts like
CrcOk & PayloadReady are not available either.
An unlimited length packet shown below is made up of the following fields:
 Preamble (1010...).
 Sync word (Network ID).
 Optional Address byte (Node ID).
 Message data
 Optional 2-bytes CRC checksum (Tx only)
DC free Data encoding
Pr eamb l e
0 to 65535
byt es
Sync W ord
0 to 8 by te s
A ddress
byt e
Message
unlimited leng t h
P ay l oad
Fields added by the packet handler in Tx and processed and removed in Rx
Message part of the payload
Optional User provided fields which are part of the payload
Figure 35. Unlimited Length Packet Format