Datasheet

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SX1272/73
WIRELESS, SENSING & TIMING DATASHEET
Rev. 2 - July 2014
©2014 Semtech Corporation
Figure 34. Fixed Length Packet Format
Variable Length Packet Format
Variable length packet format is selected when bit PacketFormat is set to 1.
This mode is useful in applications where the length of the packet is not known in advance and can vary over time. It is then
necessary for the transmitter to send the length information together with each packet in order for the receiver to operate
properly.
In this mode the length of the payload, indicated by the length byte, is given by the first byte of the FIFO and is limited to
255 bytes. Note that the length byte itself is not included in its calculation. In this mode the payload must contain at least 2
bytes i.e. length + address or message byte.
An illustration of a variable length packet is shown below. It contains the following fields:
 Preamble (1010...)
 Sync word (Network ID)
 Length byte
 Optional Address byte (Node ID)
 Message data
Message
Up to 2047 bytes
Address
byte
CRC
2-bytes
Sync Word
0 to 8 bytes
Payload
(
min 1 b
y
te
)
CRC checksum calculation
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
Optional DC free data coding
Preamble
0 to 65536 bytes