CC2510Fx / CC2511Fx
1) Read the RSSI status register
Note: It takes some time from the radio
enters RX mode until a valid RSSI value is
present in the RSSI register. Please see
DN505 [12] for details on how the RSSI
response time can be estimated.
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
The RSSI value is in dBm with ½ dB
resolution. The RSSI update rate, fRSSI
,
4) Else if RSSI_dec < 128 then RSSI_dBm
= (RSSI_dec)/2 – RSSI_offset
depends on the receiver filter bandwidth
(BWchannel defined in Section 13.6) and
AGCCTRL0.FILTER_LENGTH.
Table 68 provides typical values for the
RSSI_offset.
2⋅ BWchannel
fRSSI
=
Data Rate [kBaud]
RSSI_offset [dB]
8⋅2FILTER _ LENGTH
2.4
10
74
74
71
72
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.
250
500
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).
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]
250 kBaud, reduced current
500 kBaud
2.4 kBaud
10 kBaud
250 kBaud
Figure 52: Typical RSSI Value vs. Input Power Level for Some Typical Data Rates
13.10.4 Carrier Sense (CS)
• 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.
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).
SWRS055F
Page 195 of 241
TI [ TEXAS INSTRUMENTS ]
