NRF52811-QCAA-R datasheet(198/444 Pages) NORDIC

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Peripherals

CCA Mode 1

CCA Mode 1 is enabled by first configuring the field CCACTRL.CCAMODE=EdMode and writing the

CCACTRL.CCAEDTHRES field to a chosen value. Once the CCASTART task is written, the RADIO will

perform a ED measurement for 8 symbols and compare the measured level with that found in the

CCACTRL.CCAEDTHRES field. If the measured value is higher than or equal to this threshold, the CCABUSY

event is generated. If the measured level is less than the threshold, the CCAIDLE event is generated.

CCA Mode 2

CCA Mode 2 is enabled by configuring CCACTRL.CCAMODE=CarrierMode. The RADIO will sample to see

if a valid SFD is found during the 8 symbols. If a valid SFD is detected, the CCABUSY event is generated

and the device should not send any data. The CCABUSY event is also generated if the scan was performed

during an ongoing frame reception. In the case where the measurement period completes with no SFD

detection, the CCAIDLE event is generated. With CCACTRL.CCACORRCNT not being zero, the algorithm

will look at the correlator output in addition to the SFD detection signal. If a SFD is reported during the

scan period, it will terminate immidiately indicating busy medium. Similarly, if the number of peaks above

CCACTRL.CCACORRTHRES crosses the CCACTRL.CCACORRCNT, the CCACTRL.CCABUSY event is generated.

If less than CCACORRCOUNT crossings are found and no SFD is reported, the CCAIDLE event will be

generated and the device can send data.

CCA Mode 3

CCA Mode 3 is enabled by configuring CCACTRL.CCAMODE=CarrierAndEdMode or

CCACTRL.CCAMODE=CarrierOrEdMode, performing the required logical combination of the result from

CCA Mode 1 and 2. The CCABUSY or CCAIDLE events are generated by ANDing or ORing the energy above

threshold and carrier detection scans.

Shortcuts

An ongoing CCA can always be stopped by issuing the CCASTOP task. This will trigger the associated

CCASTOPPED event.

For CCA mode automation, a number of shortcuts are available.

• To automatically switch between RX (when performing the CCA) and to TX where the packet is sent,

the shortcut between CCAIDLE and TXEN, in conjunction with the short between CCAIDLE and STOP

muse be used.

• To automatically disable the RADIO whenever the CCA reports a busy medium, the shortcut between

CCABUSY and DISABLE can be used.

• To immediately start a CCA after ramping up into RX mode, the shortcut between RXREADY and

CCASTART can be used.

Conversion

The conversion from a CCAEDTHRES, CCA, or EDLEVEL value to dBm can be done with the following

equation, where VALHARDWARE is the hardware-reported values, being either CCAEDTHRES, CCA or

EDLEVEL, and constants ED_RSSISCALE and ED_RSSIOFFS are from electrical specifications.

PRF[dBm] = ED_RSSIOFFS + ED_RSSISCALE x VALHARDWARE

Figure 80: Conversion between hardware value and dBm

6.14.13.5 Cyclic redundancy check (CRC)

IEEE 802.15.4 uses a 16-bit ITU-T cyclic redundancy check (CRC) calculated over the MAC header (MHR)

and MAC service data unit (MSDU).

The standard defines the following generator polynomial:

4454_140 v1.0

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NRF52811-QCAA-R Datasheet(PDF) 198 Page - Nordic Semiconductor

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