CC2500-RTY1 datasheet(34/99 Pages) TI1

34 / 99 page

CC2500

SWRS040C

Page 34 of 89

The fraction of a symbol period used to

change the phase can be modified with the

DEVIATN.DEVIATION_M

setting.

This

equivalent to changing the shaping of the

symbol.

The MSK modulation format implemented in

CC2500

inverts the sync word and data

compared to e.g. signal generators.

16.3

Amplitude Modulation

The supported amplitude modulation On-Off

Keying (OOK) simply turns on or off the PA to

modulate 1 and 0 respectively.

17 Received Signal Qualifiers and Link Quality Information

CC2500 has several qualifiers that can be used

to increase the likelihood that a valid sync

word is detected.

17.1

Sync Word Qualifier

If sync word detection in RX is enabled in

CC2500 will not start

filling the RX FIFO and perform the packet

filtering described in Section 15.3 before a

valid sync word has been detected. The sync

word

qualifier

mode

set

MDMCFG2.SYNC_MODE

and is summarized in

Table 24. Carrier sense in Table 24 is

described in Section 17.4.

MDMCFG2.

SYNC_MODE

Sync Word Qualifier Mode

000

No preamble/sync

001

15/16 sync word bits detected

010

16/16 sync word bits detected

011

30/32 sync word bits detected

100

No preamble/sync, carrier sense

above threshold

101

15/16 + carrier sense above threshold

110

16/16 + carrier sense above threshold

111

30/32 + carrier sense above threshold

Table 24: Sync Word Qualifier Mode

17.2

Preamble Quality Threshold (PQT)

The Preamble Quality Threshold (PQT) sync-

word qualifier adds the requirement that the

received sync word must be preceded with a

preamble with a quality above a programmed

threshold.

Another use of the preamble quality threshold

is as a qualifier for the optional RX termination

timer. See Section 19.7 on page 43 for details.

The preamble quality estimator increases an

internal counter by one each time a bit is

received that is different from the previous bit,

and decreases the counter by 8 each time a

bit is received that is the same as the last bit.

The threshold is configured with the register

field PKTCTRL1.PQT. A threshold of 4

∙PQT for

this counter is used to gate sync word

detection. By setting the value to zero, the

preamble quality qualifier of the sync word is

disabled.

A “Preamble Quality Reached” signal can be

observed on one of the GDO pins by setting

IOCFGx.GDOx_CFG

=8. It is also possible to

determine if preamble quality is reached by

checking

the

PQT_REACHED

bit

the

PKTSTATUS

when the received signal exceeds the PQT.

17.3

RSSI

The RSSI value is an estimate of the signal

level in the chosen channel. This value is

based on the current gain setting in the RX

chain and the measured signal level in the

channel.

In RX mode, the RSSI value can be read

continuously from the RSSI status register

until the demodulator detects a sync word

(when sync word detection is enabled). At that

point the RSSI readout value is frozen until the

next time the chip enters the RX state. The

RSSI value is in dBm with ½dB resolution. The

RSSI update rate, fRSSI, depends on the

receiver filter bandwidth (BWchannel defined in

Section 13) and AGCCTRL0.FILTER_LENGTH.

LENGTH

FILTER

channel

RSSI





If PKTCTRL1.APPEND_STATUS is enabled the

RSSI

value

sync

word

detection

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