Figure 13. Generic Packet Frames Format - STMicroelectronics STM32WL5 Series Reference Manual

RM0453
The generic packet frames are illustrated in the figure below.
Variable length generic packet frame
Preamble
8 to 65535 bits
Fixed length generic packet frame
Preamble
8 to 65535 bits
1. The payload length can be extended beyond 255 bytes. Refer to
for more details.
The generic packet frames start with a preamble that is used to synchronize the receiver
with the received signal. The preamble length is programmable by Set_PacketParams()
command.
The receiver undertakes a preamble detection process that periodically restarts. For this
reason, the preamble length at the receiving side must be configured identical to the one of
the transmitting side. When the preamble length is not known at receiving side or when it
can vary, the maximum preamble length must be programmed at receiving side.
The preamble is followed by a syncword field with programmable length in
Set_PacketParams() command.
The address is optional and can be used for a unicast when several devices share the same
syncword.
In the variable length generic packet format, the syncword is followed by the length of the
payload (If the Address field is present then Length must include this additional byte),
followed by the payload and payload CRC.
In the fixed length generic packet format, the syncword is directly followed by the payload
and payload CRC.
The payload is a variable length field that contains the user data either as specified in the
variable length generic packet or in the sub-GHz radio configuration when using fixed length
generic packet by Set_PacketParams().
The payload can be followed by an optional payload CRC with programmable length in
Set_PacketParams() command.
Endianness of the frame is MSB first.

Figure 13. Generic packet frames format

Syncword Length
0 – 8 bytes
Address
Syncword
0 to 1 byte
0 – 8 bytes
RM0453 Rev 5
Sub-GHz radio (SUBGHZ)
Address
Payload
0 to 1 byte
1 to 255 bytes
CRC check
Whitening
Payload
1 to 255 bytes
CRC check
Whitening
Section 5.6: Sub-GHz radio data buffer
CRC
0 to 2 bytes
CRC
0 to 2 bytes
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