Rainbow Electronics ATmega128RFA1 - Manual (Page 70)

70
8266A-MCU Wireless-12/09
ATmega128RFA1
P
RF
= -90 + ED [dBm]
Figure 9-18. Mapping between values in PHY_ED_LEVEL and Received Input Power
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10
0 10 20 30 40 50 60 70 80 90
Register PHY_ED_LEVEL Value
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iv
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r
In
p
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P
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w
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P
R
F
[
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B
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Measured
Ideal
9.5.4.4 Interrupt Handling
The TRX24_CCA_ED_DONE interrupt is issued at the end of a manually initiated ED
measurement.
Note that an ED request should only be initiated in one of the receive states. Otherwise
the radio transceiver generates a TRX24_CCA_ED_DONE interrupt but no ED
measurement was performed.
9.5.5 Clear Channel Assessment (CCA)
The main features of the Clear Channel Assessment (CCA) module are:
• All 4 modes are available as defined by IEEE 802.15.4-2006 in section 6.9.9;
• Adjustable threshold for energy detection algorithm.
9.5.5.1 Overview
A CCA measurement is used to detect a clear channel. Four modes are specified by
IEEE 802.15.4-2006:
Table 9-21. CCA Mode Overview
CCA Mode Description
1 Energy above threshold .
CCA shall report a busy medium upon detecting any energy above the ED
threshold.
2 Carrier sense only .
CCA shall report a busy medium only upon the detection of a signal with the
modulation and spreading characteristics of an IEEE 802.15.4 compliant signal.
The signal strength may be above or below the ED threshold.