CC2550-RTY1 datasheet(19/62 Pages) TI2

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CC2550

SWRS039B

Page 19 of 58

Data Rate Programming

The data rate used when transmitting is

programmed by the MDMCFG3.DRATE_M and

the

MDMCFG4.DRATE_E

configuration

registers. The data rate is given by the formula

below. As the formula shows, the programmed

data rate depends on the crystal frequency.

()

XOSC

DRATE

DATA

DRATE

⋅

256

The following approach can be used to find

suitable values for a given data rate:

256

log

−

⋅

⎥

⎦

⎥

⎢

⎣

⎢

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛

⋅

DRATE

XOSC

DATA

XOSC

DATA

DRATE

If DRATE_M is rounded to the nearest integer

and becomes 256, increment DRATE_E and

use DRATE_M=0.

The data rate can be set from 1.2 kBaud to

500 kBaud with a minimum step size of:

Data Rate

Start

[kBaud]

Typical

Data Rate

[kBaud]

Data Rate

Stop

[kBaud]

Data Rate

Step Size

[kBaud]

0.8

1.2/2.4

3.17

0.0062

3.17

4.8

6.35

0.0124

6.35

9.6

12.7

0.0248

12.7

19.6

25.4

0.0496

25.4

38.4

50.8

0.0992

50.8

76.8

101.6

0.1984

101.6

153.6

203.1

0.3967

203.1

250

406.3

0.7935

406.3

500

1.5869

Table 16: Data Rate Step Size

Packet Handling Hardware Support

The

CC2550 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. It is not possible to only insert

preamble or only insert a sync word.

•

A CRC checksum computed over the data

field.

In a system where

CC2550 is used as the

transmitter and

CC2500 as the receiver, 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 by the use of

interleaving and coding of the data

(convolutional coding).

Note that register fields that control the packet

handling features should only be altered when

CC2550 is in the IDLE state.

13.1

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

CC2550, in combination with a

CC2500 at the receiver end, this can be done

automatically

setting

PKTCTRL0

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