Texas Instruments CC2500 User Manual

CC2500
S
WRS040
C
Page
29
of
89
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 world data often contain long sequences
of zeros and ones. Performance can then be
improved by whitening the data before
transmitting, and de
-
whitening
the data
in the
receiver. With
CC2500
, this can be done
automatically by setting
PKTCTRL0.WHITE_DATA
=1
.
All data, except
the preamble and the sync word, are then
XOR
-
ed with a 9
-
bit pseudo
-
random (PN9)
sequence before being transmitted
as shown
in
Figur
e
10
. At the receiver end, th
e data are
XOR
-
ed with the same pseudo
-
random
sequence. This way, the whitening is reversed,
and the original data appear in the receiver.
The PN9
sequence is reset to all 1’s.
Data whitening can only be used when
PKTCTRL0.CC2400_EN
=
0
(default)
.
Figur
e
10
: Data W
hiten
ing in TX M
ode
15.2
Packet Format
The format of the data packet can be
configured and consists of the following items
(see
Figure
11
)
:

Preamble

Synchronization word

Length byt
e or constant programmable
packet length

Optional address byte

Payload

Optional 2 byte CRC
Preamble bits
(1010...1010)
Sync word
Length field
Address field
Data field
CRC-16
Optional CRC-16 calculation
Optionally FEC encoded/decoded
8 x
n
bits
16/32
bits
8
bits
8
bits
8 x n bits
16
bits
Optional data whitening
Legend:
Inserted automatically in TX,
processed and removed in RX.
Optional user-provided fields processed in TX,
processed but not removed in RX.
Unprocessed user data (apart from FEC
and/or whitening)
Figure
11
: Packet F
ormat

Texas Instruments CC2500 Specifications

General

Brand	Texas Instruments
Model	CC2500
Category	Transceiver
Language	English