MRF89XAM8A-I Datasheet, PDF (83/140 Pages) Microchip Technology – Ultra Low-Power, Integrated ISM Band Sub-GHz Transceiver

MRF89XA
3.11.0.3 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 3-27, is given by the first byte of
the FIFO and is limited only by the width of the FIFO
selected. In this mode, the payload must contain at
least 2 bytes (that is, length plus address or message
byte).
A variable length packet frame format is illustrated in
Figure 3-27, which contains the following fields:
• Preamble (1010...)
• Sync word (Network ID)
• Length byte
• Optional Address byte (Node ID)
• Message data
• Optional 2-bytes CRC checksum
Note: The length byte is not included in the CRC
calculation.
FIGURE 3-27:
VARIABLE LENGTH PACKET FORMAT
Optional DC free data coding
CRC checksum calculation
Length
Preamble
1 to 4 bytes
Sync Word
1 to 4 bytes
Length
byte
Address
Message
byte ^{0 to (FIFO size - 1) bytes}
CRC
2-bytes
Payload/FIFO
Fields added by the packet handler in TX and processed and removed in RX
Optional, user provided fieldhich are part of the payload
Message part of the payload
© 2010–2011 Microchip Technology Inc.
Preliminary
DS70622C-page 83