Texas Instruments SimpleLink CC2620 Technical Reference Manual page 1536

IEEE 802.15.4
The overall CCA state ccaState depends on the ccaEnEnergy, ccaEnCorr, and ccaEnSync bits of ccaOpt
together with the ccaCorrOp and ccaSyncOp bits. The following rules apply for finding the ccaState
(ccaTmp is a helper state in the description):
• If ccaEnEnergy = 0 and ccaEnCorr = 0 and ccaEnSync = 0, then ccaState = IDLE
• If ccaEnEnergy = 1 and ccaEnCorr = 0, then ccaTmp = ccaEnergy
• If ccaEnEnergy = 0 and ccaEnCorr = 1, then ccaTmp = ccaCorr
• If ccaEnEnergy = 1 and ccaEnCorr = 1 and ccaCorrOp = 0, then:
– If either ccaEnergy or ccaCorr is BUSY, then ccaTmp = BUSY;
– Otherwise, if either ccaEnergy or ccaCorr is INVALID, then ccaTmp = INVALID;
– Otherwise, ccaTmp = IDLE
• If ccaEnEnergy = 1 and ccaEnCorr = 1 and ccaCorrOp = 1, then:
– If either ccaEnergy or ccaCorr is IDLE, then ccaTmp = IDLE;
– Otherwise, if either ccaEnergy or ccaCorr is Invalid, then ccaTmp = INVALID;
– Otherwise, ccaTmp = BUSY
• If ccaEnEnergy = 0 and ccaEnCorr = 0 and ccaEnSync = 1, then ccaState = ccaSync
• Otherwise, if ccaEnSync = 1 and ccaSyncOp = 0, then:
– If either ccaTmp or ccaSync is BUSY, then ccaState = BUSY;
– Otherwise, if ccaTmp is Invalid, then ccaState = INVALID;
– Otherwise, ccaState = IDLE
• Otherwise, if ccaEnSync = 1 and ccaSyncOp = 1, then:
– If either ccaTmp or ccaSync is IDLE, then ccaState = IDLE;
– Otherwise, if ccaTmp is INVALID, then ccaState = INVALID;
– Otherwise, ccaState = BUSY
The ccaSync CCA state is required to be Idle for the overall CCA state to be IDLE, according to the IEEE
802.15.4 standard. Thus, to comply, ccaEnSync is 1 and cceSyncOp is 0.
CCA mode 1, as defined in the IEEE 802.15.4 standard, is implemented by setting ccaEnEnergy = 1 and
ccaEnCorr = 0. CCA mode 2 is implemented by setting ccaEnEnergy = 0 and ccaEnCorr = 1. CCA mode
3 is implemented by setting ccaEnEnergy = 1 and ccaEnCorr = 1. With CCA mode 3, ccaCorrOp is
allowed to be either 0 or 1; this distinguishes between the logical operator AND (1) and OR (0) as
described in the IEEE 802.15.4 standard.
The CCA states and the current RSSI can be read by the system CPU by issuing the immediate
command CMD_IEEE_CCA_REQ. If a CMD_IEEE_CSMA operation is running in the foreground, the
radio CPU also monitors the CCA autonomously.
23.5.4.2 Energy Detect Scan Operation
The energy detect scan radio operation is a background-level operation that starts with the
CMD_IEEE_ED_SCAN command, and uses a command structure as given in
At the start of an RX operation, the radio CPU waits for the start trigger, then programs the frequency
based on the channel parameter. If channel is 0xFF, the operation keeps running on an already-
configured channel. This requires that the operation follows another receive operation or a synthesizer
programming operation. If the frequency synthesizer is not running, the operation ends with an error. After
programming the frequency, the radio CPU configures the receiver to receive IEEE 802.15.4 packets, but
it does not store any received data.
While the receiver is running, CCA is updated as described in
obtains sync on a frame, the PHY header is read. This is used only for determining the carrier sense
based on sync found, and sync search restarts immediately afterwards.
The energy detect scan operation ends under the same conditions as the RX operation, as described in
Section 23.5.4.1.4. Before the operation ends, the radio CPU writes the maximum-observed RSSI during
the energy detect scan operation to maxRssi.
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Radio
Copyright © 2015, Texas Instruments Incorporated
Table 23-60.
Section 23.5.4.1.5. When the demodulator
SWCU117C – February 2015 – Revised September 2015
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