NRF52820-QDAA-R datasheet(183/437 Pages) NORDIC

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Peripherals

RXRU

RXIDLE

SHR

PAYLOAD

CRC

RXIDLE

RXDISABLE

’X’

Figure 73: IEEE 802.15.4 receive sequence

When a valid SHR is received, the RADIO will start storing future octets (starting with PHR) to the data

memory pointed to by PACKETPTR. After the SFD octet is received, the FRAMESTART event is generated.

If the CRC module is enabled it will start updating with the second byte received (first byte in payload)

and run for the full frame length. The two last bytes in the frame are not written to RAM when CRC is

configured. However, if the result of the CRC after running the full frame is zero, the CRCOK event will

be generated. The END event is generated when the last octet has been received and is available in data

memory.

When a packet is received, a link quality indicator (LQI) is also generated and appended immediately after

the last received octet. When using an IEEE 802.15.4 compliant frame, this will be just after the MSDU

since the FCS is not reported. In the case of a non-compliant frame, it will be appended after the full

frame. The LQI reported by hardware must be converted to IEEE 802.15.4 range by an 8-bit saturating

multiplication of 4, as shown in IEEE 802.15.4 ED measurement example on page 179. The LQI is only

valid for frames equal to or longer than three octets. When receiving a frame, the RSSI (reported as

negative dB) will be measured at three points during the reception. These three values will be sorted and

the middle one selected (median 3) to be remapped within the LQI range. The following figure illustrates

the LQI measurement and how the data is arranged in data memory.

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NRF52820-QDAA-R Datasheet(PDF) 183 Page - Nordic Semiconductor