Data Sheet

LJ1269HC
Rev1.0 Page 50 Web: www.ljelect.com
The length of the payload is limited to 255 bytes if AES is not enabled else the message is limited to 64 bytes (i.e. max 65 bytes
payload if Address byte is enabled).
The length programmed in PayloadLength 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 below. It contains the following fields:
 Preamble (1010...)
 Sync word (Network ID)
 Optional Address byte (Node ID)
 Message data
 Optional 2-bytes CRC checksum
Figure 32. 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 if AES is not enabled else the message is limited to 64 bytes (i.e. max 66 bytes payload if Address byte is enabled). 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
 Optional 2-bytes CRC checksum
Sub GHz FSK/OOK Transceiver Module DATASHEET