SM1212E433 Datasheet, PDF (50/77 Pages) Semtech Corporation – Ultra-Low Power Integrated 300-510MHz Transceiver

SX1212
ADVANCED COMMUNICATIONS & SENSING
The length stored in this register relates only to the payload which includes the message and the optional address
byte. In this mode, the payload must contain at least one byte, i.e. address or message byte.
An illustration of a fixed length packet is shown in Figure 43. It contains the following fields:
ƒ Preamble (1010...).
ƒ Sync word (Network ID).
ƒ Optional Address byte (Node ID).
ƒ Message data.
ƒ Optional 2-bytes CRC checksum.
Optional DC free data coding
CRC checksum calculation
Preamble Sync Word Address
1 to 4 bytes 1 to 4 bytes
byte
Message
0 to (FIFO size) bytes
CRC
2-bytes
Payload/FIFO
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 43: Fixed Length Packet Format
5.5.2.2. Variable Length Packet Format
This mode is necessary 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 in Figure 44, is given by the first byte of the
FIFO and is limited only by the width of the FIFO selected. 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 in Figure 44. It contains the following fields:
ƒ Preamble (1010...).
ƒ Sync word (Network ID).
ƒ Length byte
ƒ Optional Address byte (Node ID).
ƒ Message data.
ƒ Optional 2-bytes CRC checksum.
Rev 2 – June 18th, 2009
Page 50 of 77
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