CC2520_17 Datasheet, PDF (120/134 Pages) Texas Instruments – 2.4 GHZ IEEE 802.15.4/ZIGBEE RF TRANSCEIVER

CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
CCACTRL0, A 0x036, R 0xE0, CCA threshold
Bit
Bit mnemonic
no.
7:0
CCA_THR[7:0]
Reset
value
0xE0
Mode
R/W
Description
Clear Channel Assessment threshold value, signed 2’s
complement number for comparison with the RSSI.
The unit is 1 dB, offset is about 76dBm. The CCA signal goes
high when the received signal is below this value. The CCA signal
is available on the CCA pin and in FSMSTAT1 register.
Note that the value should never be set lower than CCA_HYST-
128 in order to avoid erroneous behavior of the CCA signal.
NOTE
The reset value translates to an input level of approximately -32 –
76 = -108 dBm, which is well below the sensitivity limit. That
means the CCA signal will never indicate a clear channel.
This register should be updated to 0xF8, which translates to an
input level of about -8 - 76 = -84dBm.
CCACTRL1, A 0x037, R 0x1A, Other CCA options
Bit
Bit mnemonic
no.
7:5
RESERVED
4:3
CCA_MODE[1:0]
2:0
CCA_HYST[2:0]
Reset
value
000
11
010
Mode
R0
R/W
R/W
Description
Read as zero
00 : CCA always set to ‘1’
01 : CCA = ‘1’ when RSSI < CCA_THR-CCA_HYST, CCA = ‘0’
when RSSI >= CCA_THR
10 : CCA = ‘1’ when not receiving a frame, else CCA = ‘0’
11 : CCA = ‘1’ when RSSI < CCA_THR-CCA_HYST and not
receiving a frame, CCA=0 when RSSI >= CCA_THR or receiving a
frame
Sets the level of CCA hysteresis. Unsigned values given in dB.
RSSI, A 0x038, R 0x80, RSSI status register
Bit
Bit mnemonic
no.
7:0
RSSI_VAL[7:0]
Reset
value
0x80
Mode
R
Description
RSSI estimate on a logarithmic scale, signed number on 2’s
complement.
Unit is 1 dB, offset is TBD [depends on the absolute gain of the
RX chain, including external components, and should be
measured]. The RSSI value is averaged over 8 symbol periods.
The RSSI_VALID status bit should be checked before reading
RSSI_VAL the first time.
The reset value of –128 also indicates that the RSSI value is
invalid.
RSSISTAT, A 0x039, R 0x00, RSSI valid status register
Bit
Bit mnemonic
no.
7:1
RESERVED
0
RSSI_VALID
Reset
value
0000
000
0
Mode
R0
R
Description
Read as zero
RSSI value is valid. Occurs eight symbol periods after entering
RX
120
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