NRF52811-QCAA-R datasheet(197/444 Pages) NORDIC

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Peripherals

For scaling between hardware value and dBm, see equation Conversion between hardware value and dBm

on page 198.

The mlme-scan.req primitive of the MAC layer uses the ED measurement to detect channels where there

might be wireless activity. To assist this primitive, a tailored mode of operation is available where the

ED measurement runs for a defined number of iterations keeping track of the maximum ED level. This is

enganged by writing the EDCNT register to a value different from 0, where it will run the specified number

of iterations and report the maximum energy measurement in the EDSAMPLE register. The scan is started

with EDSTART task and its end indicated with the EDEND event. This significantly reduces the interrupt

frequency and therefore power consumption. The following figure shows how the ED measurement will

operate depending on the EDCNT register.

128 µs

EDCNT = 0

EDSTART

EDEND

Scan 0

EDCNT = N-1

EDSTART

EDEND

Scan 1

Scan N-1

...

128*(N) µs

Figure 79: Energy detection measurement examples

The scan is stopped by writing the EDSTOP task. It will be followed by the EDSTOPPED event when the

module has terminated.

6.14.13.4 Clear channel assessment (CCA)

IEEE 802.15.4 implements a listen-before-talk channel access method to avoid collisions when

transmitting, known as carrier sense multiple access with collision avoidance (CSMA-CA). The key part of

this is measuring if the wireless medium is busy or not.

The following clear channel assesment modes are supported:

• CCA Mode 1 (energy above threshold): The medium is reported busy upon detecting any energy above

the ED threshold.

• CCA Mode 2 (carrier sense only): The medium is reported busy upon detection of a signal compliant

with the IEEE 802.15.4 standard with the same modulation and spreading characteristics.

• CCA Mode 3 (carrier sense with energy above threshold): The medium is reported busy using a logical

combination (AND/OR) between the results from CCA Mode 1 and CCA Mode 2.

The clear channel assessment should survey a period equal to 8 symbols or 128 µs.

The RADIO must be in receive mode and be able to receive correct packets when performing the CCA. The

shortcut between READY and START must be disabled if baseband processing is not to be performed while

the measurement is running.

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