mrf89xa Microchip Technology Inc., mrf89xa Datasheet - Page 87

• Manufacturer Part Number: mrf89xa
• Description: Ultra-low Power, Integrated Ism Band Sub-ghz Transceiver
• Manufacturer: Microchip Technology Inc.

3.11.0.3
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).
FIGURE 3-27:
© 2010 Microchip Technology Inc.
Variable Length Packet Format
1 to 4 bytes
Preamble
Optional User provided fields which are part of the payload
Message part of the payload
Fields added by the packet handler in TX and processed and removed in RX
VARIABLE LENGTH PACKET FORMAT
1 to 4 bytes
Sync Word
Length
byte
Preliminary
CRC checksum calculation
Address
Optional DC free data coding
byte
Payload/FIFO
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
0 to (FIFO size - 1) bytes
Note:
Length
Message
The length byte is not included in the CRC
calculation.
MRF89XA
2-bytes
CRC
DS70622B-page 87