CC1021-RTR1 datasheet(36/91 Pages) TI1

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Not Recommended for New Designs NRND

CC1021

SWRS045D – JANUARY 2006 – REVISED JANUARY 2015

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5.9.10 Preamble Length and Sync Word

The rules for choosing a good sync word are as follows:

1. The sync word should be significantly different from the preamble.

2. A large number of transitions is good for the bit synchronization or clock recovery. Equal bits reduce

the number of transitions. The recommended sync word has at the most 3 equal bits in a row.

3. Autocorrelation. The sync word should not repeat itself, as this will increase the likelihood for errors.

4. In general the first bit of sync should be opposite of last bit in preamble, to achieve one more transition.

The recommended sync words for CC1021 are 2 bytes (D391), 3 bytes (D391DA) or 4 bytes (D391DA26)

and are selected as the best compromise of the above criteria.

Using the register settings provided by the SmartRF Studio software, packet error rates (PER) less than

0.5% can be achieved when using 24 bits of preamble and a 16 bit sync word (D391). Using a preamble

longer than 24 bits will improve the PER.

When performing the PER measurements described above the packet format consisted of 10 bytes of

random data, 2 bytes CRC and 1 dummy byte in addition to the sync word and preamble at the start of

each package.

For the test, 1000 packets were sent 10 times. The transmitter was put in power down between each

packet. Any bit error in the packet, either in the sync word, in the data or in the CRC caused the packet to

be counted as a failed packet.

5.9.11 Carrier Sense

The carrier sense signal is based on the RSSI value and a programmable threshold. The carrier sense

function can be used to simplify the implementation of a CSMA (Carrier Sense Multiple Access) medium

access protocol.

Carrier

sense

threshold

level

programmed

CS_LEVEL[4:0]

the

VGA4

and

VGA_SETTING[4:0] in the VGA3 register.

VGA_SETTING[4:0] sets the maximum gain in the VGA. This value must be set so that the ADC works

with optimum dynamic range for a certain channel filter bandwidth. The detected signal strength (after the

ADC) will therefore depend on this setting.

CS_LEVEL[4:0] sets the threshold for this specific VGA_SETTING[4:0] value. If the VGA_SETTING[4:0] is

changed, the CS_LEVEL[4:0] must be changed accordingly to maintain the same absolute carrier sense

threshold. See Figure 5-17 for an explanation of the relationship between RSSI, AGC and carrier sense

settings.

The carrier sense signal can be read as the CARRIER_SENSE bit in the STATUS register.

The carrier sense signal can also be made available at the LOCK pin by setting LOCK_SELECT[3:0] =

0100 in the LOCK register.

Detailed Description

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CC1021-RTR1 Datasheet(PDF) 36 Page - Texas Instruments

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