CC2500-RTY1 datasheet(32/84 Pages) TI

32 / 84 page

CC2500

PRELIMINARY Data Sheet (Rev.1.2)

SWRS040A

Page 32 of 83

If PKTCTRL1.APPEND_STATUS is enabled the

RSSI value at sync word detection is

automatically added to the first byte appended

after the data.

The RSSI value read from the RSSI status

following procedure can be used to convert the

RSSI reading to an absolute power level

(RSSI_dBm).

1) Read the RSSI status register

2) Convert the reading from a hexadecimal

number to a decimal number (RSSI_dec)

3) If RSSI_dec ≥ 128 then RSSI_dBm =

(RSSI_dec - 256)/2 – RSSI_offset

4) Else if RSSI_dec < 128 then RSSI_dBm =

(RSSI_dec)/2 – RSSI_offset

Table 25 provides typical values for the

RSSI_offset.

Figure 13 shows typical plots of RSSI readings

as a function of input power level for different

data rates.

Data rate

[kbps]

RSSI_offset [decimal]

2.4

250

500

Table 25: Typical RSSI_offset values

-120.0

-110.0

-100.0

-90.0

-80.0

-70.0

-60.0

-50.0

-40.0

-30.0

-20.0

-10.0

0.0

-120

-110

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

Input pow er [dBm]

2.4 kbps

10 kbps

250 kbps

250 kbps, reduced current

500 kbps

Figure 13: Typical RSSI value vs. input power level for some typical data rates

17.4

Carrier Sense (CS)

The Carrier Sense flag is used as a sync word

qualifier and for CCA. The CS flag can be set

based on two conditions, which can be

individually adjusted:

•

CS is asserted when the RSSI is above a

programmable absolute threshold, and de-

asserted when RSSI is below the same

threshold (with hysteresis).

•

CS is asserted when the RSSI has

increased with a programmable number of

dB from one RSSI sample to the next, and

de-asserted when RSSI has decreased

with the same number of dB. This setting

is not dependent on the absolute signal

level and is thus useful to detect signals in

environments with a time varying noise

floor.

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