NRF52820-QDAA-R datasheet(182/437 Pages) NORDIC

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Peripherals

PAYLOAD

CRC

RXRU

Clear channel

TXRU

TXIDLE

SHR

TXDISABLE

RXIDLE

Figure 72: IEEE 802.15.4 transmit sequence

The receiver will ramp up and enter the RXIDLE state where the READY event is generated. Upon receiving

the ready event, the CCA is started by triggering the CCASTART task. The chosen mode of assessment

(CCACTRL.CCAMODE register) will be performed and signal the CCAIDLE or CCABUSY event 128 µs later. If

the CCABUSY event is received, the RADIO will have to retry the CCA after a specific back-off period. This is

outlined in the IEEE 802.15.4 standard, Figure 69 in section 7.5.1.4 The CSMA-CA algorithm.

If the CCAIDLE event is generated, a write to the TXEN task register enters the RADIO in TXRU state.

The READY event will be generated when the RADIO is in TXIDLE state and ready to transmit. With the

PACKETPTR pointing to the length (PHR) field of the frame, the START task can be written. The RADIO will

send the four octet preamble sequence followed by the start of frame delimiter (SFD register). The first

byte read from the Data RAM is the length field (PHR) followed by the transmission of the number of

bytes indicated as the frame length. If the CRC module is configured it will run for PHR-2 octets. The last

two octets will be substituted with the results from running the CRC. The necessary CRC parameters are

sampled on the START task. The FCS field of the frame is little endian.

In addition to the already available shortcuts, one is provided between READY event and CCASTART task so

that a CCA can automatically start when the receiver is ready. A second shortcut has been added between

CCAIDLE event and the TXEN task, so that upon detecting a clear channel the RADIO can immediately

enter transmit mode.

6.12.13.7 Receive sequence

The reception is started by first putting the RADIO in receive mode. After writing to the RXEN task, the

RADIO will start ramping up and enter the RXRU state.

When the READY event is generated, the RADIO enters the RXIDLE mode. For the baseband processing to

be enabled, the START task must be written. An outline of the IEEE 802.15.4 reception can be found in the

following figure.

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