CC2510_15 Datasheet, PDF (195/245 Pages) Texas Instruments – Low-Power SoC (System-on-Chip) with MCU, Memory,2.4 GHz RF Transceiver, and USB Controller

CC2511F8 - Not Recommended for New Designs
The RSSI value is in dBm with ½ dB
resolution. The RSSI update rate, f_RSSI,
depends on the receiver filter bandwidth
(BW_channel defined in Section 13.6) and
AGCCTRL0.FILTER_LENGTH.
f _RSSI
=
2 ⋅ BW_channel
8 ⋅ 2^{FILTER _ LENGTH}
If PKTCTRL1.APPEND_STATUS is enabled the
RSSI value at sync word detection is
automatically added to the first byte appended
after the data payload.
The RSSI value read from the RSSI status
register is a 2’s complement number. The
following procedure can be used to convert the
RSSI reading to an absolute power level
(RSSI_dBm).
1) Read the RSSI status register
CC2510Fx / CC2511Fx
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 68 provides typical values for the
RSSI_offset.
Data Rate [kBaud]
2.4
10
250
500
RSSI_offset [dB]
74
74
71
72
Table 68: Typical RSSI_offset Values
Figure 52 shows typical plots of RSSI readings
as a function of input power level for different
data rates.
0.0
-10.0
-20.0
-30.0
-40.0
-50.0
-60.0
-70.0
-80.0
-90.0
-100.0
-110.0
-120.0
-120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0
Input power [dBm]
2.4 kBaud
10 kBaud
250 kBaud
250 kBaud, reduced current
500 kBaud
Figure 52: Typical RSSI Value vs. Input Power Level for Some Typical Data Rates
13.10.4 Carrier Sense (CS)
The Carrier Sense (CS) 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.
Carrier Sense can be used as a sync word
qualifier that requires the signal level to be
higher than the threshold for a sync word
search to be performed. The signal can also
be observed on P1_5, P1_6, or P1_7 by
SWRS055G
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