CC2500-RTR1 datasheet(29/99 Pages) TI1

29 / 99 page

CC2500

SWRS040C

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

the

receiver

uniform

operation conditions (no data dependencies).

Real world data often contain long sequences

of zeros and ones. Performance can then be

improved

whitening

the

data

before

transmitting, and de-whitening the data in the

receiver. With

CC2500, this can be done

automatically

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 Figure 10. At the receiver end, the 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).

Figure 10: Data Whitening in TX Mode

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 byte or constant programmable

packet length



Optional address byte



Payload



Optional 2 byte CRC

Preamble bits

(1010...1010)

Data field

Optional CRC-16 calculation

Optionally FEC encoded/decoded

8 x n bits

16/32 bits

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 Format

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