NXP Semiconductors MKW01Z128, Reference Manual

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Transceiver Digital Control and Communications
MKW01xxRM Reference Manual, Rev. 3, 04/2016
Freescale Semiconductor, Inc. 7-11
Figure 7-10. Fixed Length Packet Format
7.5.2.2 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. 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
Figure 7-11. Variable Length Packet Format
Message
Up to 255 bytes
Address
byte
CRC
2-bytes
Sync Word
0 to 8 bytes
Preamble
0 to 65535
bytes
Payload
(min 1 byte)
CRC checksum calculation
DC free Data encoding
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
AES Enc/Dec
Message
Up to 255 bytes
Address
byte
Length
byte
CRC
2-bytes
Sync Word
0 to 8 bytes
Preamble
0 to 65535
bytes
Payload
(min 2 bytes)
CRC checksum calculation
DC free Data encoding
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
AES Enc/Dec