Rainbow Electronics RF22 - Manual (Page 25)

RF22
Version: 0.1 Date: 12/23/2008
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"Register 30h. Data Access Control" through "Register 49h. Received Header 1" are used to set the different fields in
the packet structure. Automatically adding these fields to the data payload greatly reduces the amount of
communication between the microcontroller and the RF22 and therefore also reduces the required computational
power of the microcontroller.
The general packet structure is shown in Figure 16. The length of each field is shown below the field. The preamble
pattern is always a series of alternating ones and zeroes, starting with a one. All the fields have programmable lengths
to accommodate different applications. The most common CRC polynominals are available for selection.
Data
Preamble
Syn
c Word
T
X
Head
er
P
ack
et L
e
ngt
h
CRC
1-512 Bytes 1-4 Bytes
0-4Byte
0 or 1 Byt
e 0 or 2
Bytes
Figure16. Packet Structure
An overview of the packet handler configuration registers is shown in Table 14. A complete register description can be
found in “12.1. Complete Register Table and Descriptions”.
6.3. Packet Handler TX Mode
If the TX packet length is set the packet handler will send the number of bytes in the packet length field before returning
to ready mode and asserting the packet sent interrupt. To resume sending data from the FIFO the microcontroller
needs to command the chip to re-enter TX mode. Figure 17 provides an example transaction where the packet length
is set to three bytes.
⎪
⎭
⎪
⎬
⎫
3
2
1
data
data
data
This will be send in the first transmission
⎪
⎭
⎪
⎬
⎫
6
5
4
data
data
data
This will be send in the second transmission
⎪
⎭
⎪
⎬
⎫
9
8
7
data
data
data
This will be send in the third transmission
Figure17. Multiple Packets in TX Packet Handler
6.4. Packet Handler RX Mode
6.4.1. Packet Handler Disabled
When the packet handler is disabled certain portions of the packet handler are still required. Proper modem operation
requires preamble and sync, as shown in Figure 18. Bits after sync will be treated as raw data with no qualification.
This mode allows for the creation of a custom packet handler when the automatic qualification parameters are not
sufficient. Manchester encoding is supported but the use of data whitening, CRC, or header checks is not.
Preamble
DATA
SYNC
Figure18. Required RX Packet Structure with Packet Handler Disabled