CC2550_13 Datasheet, PDF (19/61 Pages) Texas Instruments – Low-Cost Low-Power 2.4 GHz RF Transmitter

CC2550
12 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.
( ) _{RDATA =}
256 + DRATE _ M
2²⁸
⋅ 2^{DRATE _ E} _{⋅ f XOSC}
The following approach can be used to find
suitable values for a given data rate:
DRATE
_
E
=
⎢
⎢^log
⎢⎣
2
⎜⎜⎝⎛
R_DATA ⋅ 2 ²⁰
f _XOSC
⎟⎟⎠⎞⎥⎥⎦⎥
DRATE _ M = ^{RDATA ⋅ 228} − 256
f _XOSC ⋅ 2 ^{DRATE _ E}
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]
0.8
3.17
6.35
12.7
25.4
50.8
101.6
203.1
406.3
Typical
Data Rate
[kBaud]
1.2/2.4
4.8
9.6
19.6
38.4
76.8
153.6
250
500
Data Rate
Stop
[kBaud]
3.17
6.35
12.7
25.4
50.8
101.6
203.1
406.3
500
Data Rate
Step Size
[kBaud]
0.0062
0.0124
0.0248
0.0496
0.0992
0.1984
0.3967
0.7935
1.5869
Table 16: Data Rate Step Size
13 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 by setting PKTCTRL0
SWRS039B
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