CC1100-RTY1 datasheet(31/100 Pages) TI1

31 / 100 page

CC1100

SWRS038D

Page 31 of 92

14.3

Byte Synchronization

Byte synchronization is achieved by a

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, a 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 37 for more details.

Packet Handling Hardware Support

The

CC1100 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.

•

addition,

the

following

can

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).

•

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

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

Indicating the link quality

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

CC1100 is in the IDLE state.

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 in the receiver uniform

operation conditions (no data dependencies).

CC1100-RTY1 Datasheet(PDF) 31 Page - Texas Instruments

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