CC2550-RTR1 datasheet(18/55 Pages) TI

18 / 55 page

CC2550

PRELIMINARY Data Sheet (Rev.1.2)

SWRS039A

Page 18 of 54

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 programmed from 1.2 kbps

to 500 kbps with a minimum step size of:

Data rate

start

[kbps]

Typical

data rate

[kbps]

Data rate

stop [kbps]

Data rate

step size

[kbps]

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 will 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.

•

Optionally whiten the data with a PN9

sequence.

•

Optionally Interleave and Forward Error

Code the data.

•

Optionally compute and add a CRC

checksum 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 kbps data rate

where the recommended preamble length is 8

bytes.

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 in the receiver.

With

CC2550, in combination with a CC2500 at

the

receiver

end,

this

can

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 9.

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.

Data whitening can only be used when

PKTCTRL0.CC2400_EN

= 0 (default).

CC2550-RTR1 数据表(PDF) 18 Page - Texas Instruments

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