CC1101
SWRS061H Page 37 of 98
15 Packet Handling Hardware Support
The
CC1101
has built-in hardware support for
packet oriented radio protocols.
In transmit mode, the packet handler can be
configured to add the following elements to the
packet stored in the TX FIFO:
A programmable number of preamble
bytes
A two byte synchronization (sync) word.
Can be duplicated to give a 4-byte sync
word (recommended). It is not possible to
only insert preamble or only insert a sync
word
A CRC checksum computed over the data
field.
The recommended setting is 4-byte preamble
and 4-byte sync word, except for 500 kBaud
data rate where the recommended preamble
length is 8 bytes. In addition, the following can
be implemented on the data field and the
optional 2-byte CRC checksum:
Whitening of the data with a PN9
sequence
Forward Error Correction (FEC) by the use
of interleaving and coding of the data
(convolutional coding)
In receive mode, the packet handling support
will de-construct the data packet by
implementing the following (if enabled):
Preamble detection
Sync word detection
CRC computation and CRC check
One byte address check
Packet length check (length byte checked
against a programmable maximum length)
De-whitening
De-interleaving and decoding
Optionally, two status bytes (see Table 27 and
Table 28) with RSSI value, Link Quality
Indication, and CRC status can be appended
in the RX FIFO.
Table 27: Received Packet Status Byte 1
(first byte appended after the data)
1: CRC for received data OK
(or CRC disabled)
0: CRC error in received data
Indicating the link quality
Table 28: Received Packet Status Byte 2
(second byte appended after the data)
15.1 Data Whitening
From a radio perspective, the ideal over the air
data are random and DC free. This results in
the smoothest power distribution over the
occupied bandwidth. This also gives the
regulation loops in the receiver uniform
operation conditions (no data dependencies).
Real data often contain long sequences of
zeros and ones. In these cases, performance
can be improved by whitening the data before
transmitting, and de-whitening the data in the
receiver.
With
CC1101
, this can be done automatically.
By setting PKTCTRL0.WHITE_DATA=1, all
data, except the preamble and the sync word
will be XOR-ed with a 9-bit pseudo-random
(PN9) sequence before being transmitted. This
is shown in Figure 18. At the receiver end, the
data are XOR-ed with the same pseudo-
random sequence. In this way, the whitening is
reversed, and the original data appear in the
receiver. The PN9 sequence is initialized to all
1‟s.
Note: Register fields that control the
packet handling features should only be
altered when
CC1101
is in the IDLE state.
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