CC2500-RTR1 datasheet(28/99 Pages) TI1

28 / 99 page

CC2500

SWRS040C

Page 28 of 89

14.3

Byte Synchronization

Byte

synchronization

achieved

continuous sync word search. The sync word

is a 16 bit configurable field (can be repeated

to get a 32 bit) that is automatically inserted at

the start of the packet by the modulator in

transmit mode. The demodulator uses this

field to find the byte boundaries in the stream

of bits. The sync word will also function as a

system identifier, since only packets with the

correct predefined sync word will be received if

the sync word detection in RX is enabled in

sync word detector correlates against the

user-configured 16 or 32 bit sync word. The

correlation threshold can be set to 15/16,

16/16, or 30/32 bits match. The sync word can

be further qualified using the preamble quality

indicator mechanism described below and/or a

carrier sense condition. The sync word is

configured through the SYNC1 and SYNC0

registers.

In order to make false detections of sync

words

less

likely,

mechanism

called

preamble quality indication (PQI) can be used

to qualify the sync word. A threshold value for

the preamble quality must be exceeded in

order for a detected sync word to be accepted.

See Section 17.2 on page 34 for more details.

15 Packet Handling Hardware Support

The

CC2500 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 (recommended). It is not possible to

only insert preamble or only insert a sync

word.



A CRC checksum computed over the data

field

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

the

data

with

PN9

sequence.



Forward error correction by the use of

interleaving

and

coding

the

data

(convolutional coding).

In receive mode, the packet handling support

will

de-construct

the

data

packet

implementing the following (if enabled):



Preamble detection



Sync word detection



CRC computation and CRC check



One byte address check



Packet length check (length byte checked

against a programmable maximum length)



De-whitening



De-interleaving and decoding

Optionally, two status bytes (see Table 21 and

Table 22) with RSSI value, Link Quality

Indication, and CRC status can be appended

in the RX FIFO.

Bit

Field Name

Description

7:0

RSSI

RSSI value

Table 21: Received Packet Status Byte 1

(first byte appended after the data)

Bit

Field Name

Description

CRC_OK

1: CRC for received data OK (or

CRC disabled)

0: CRC error in received data

6:0

LQI

The Link Quality Indicator

estimates how easily a received

signal can be demodulated

Table 22: Received Packet Status Byte 2

(second byte appended after the data)

Note that register fields that control the packet

handling features should only be altered when

CC2500 is in the IDLE state.

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