MRF24J40_08 Datasheet, PDF (91/152 Pages) Microchip Technology – IEEE 802.15.4™ 2.4 GHz RF Transceiver

MRF24J40
3.5 Clear Channel Assessment (CCA)
The CCA signal is an indication to the MAC layer from
the PHY layer as to whether the medium is busy or idle.
The MRF24J40 provides three methods of performing
CCA. Refer to IEEE 802.15.4-2003 Standard,
Section 6.7.9 “CCA”.
3.5.1
CCA MODE 1: ENERGY ABOVE
THRESHOLD
CCA reports a busy medium upon detecting energy
above the Energy Detection (ED) threshold.
1. Program CCAEDTH 0x3A<7:6> to the value, ‘10’.
2. Program CCAMODE 0x3F<7:0> with CCA ED
threshold value (RSSI value).
The 8-bit CCAEDTH threshold can be mapped
to a power level according to RSSI. Refer
to Section 3.6 “Received Signal Strength
Indicator (RSSI)/Energy Detection (ED)”.
3.5.2
CCA MODE 2: CARRIER SENSE
ONLY
CCA reports a busy medium only upon detection of a
signal with the modulation and spreading characteris-
tics of IEEE 802.15.4. This signal may or may not be
above the ED threshold.
1. Program CCAMODE 0x3A<7:6> to the value, ‘01’.
2. Program CCACSTH 0x3A<5:2> with the CCA
carrier sense threshold (units).
3.5.3
CCA MODE 3: CARRIER SENSE
WITH ENERGY ABOVE
THRESHOLD
CCA reports a busy medium only upon detection of a
signal with modulation or spreading characteristics of
IEEE 802.15.4 with energy above the ED threshold.
1. Program CCAMODE 0x3A<7:6> to the value,
‘11’.
2. Program CCACSTH 0x3A<5:2> with the CCA
carrier sense threshold.
3. Program CCAEDTH 0x3F<7:0> with the CCA
ED threshold.
The 8-bit CCAEDTH threshold can be mapped
to a power level according to RSSI. Refer
to Section 3.6 “Received Signal Strength
Indicator (RSSI)/Energy Detection (ED)”.
TABLE 3-6: REGISTERS ASSOCIATED WITH CCA
Addr. Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0x3A BBREG2 CCAMODE1 CCAMODE0 CCACSTH3 CCACSTH2 CCACSTH1 CCACSTH0
r
r
0x3F CCAEDTH CCAEDTH7 CCAEDTH6 CCAEDTH5 CCAEDTH4 CCAEDTH3 CCAEDTH2 CCAEDTH1 CCAEDTH0
© 2008 Microchip Technology Inc.
Preliminary
DS39776B-page 89