NRF52820-QDAA-R datasheet(177/437 Pages) NORDIC

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Peripherals

The preamble sequence consists of four octets that are all zero, and are used for synchronizing the

RADIO's receiver. Following the preamble is the single octet start of frame delimiter (SFD), with a fixed

value of 0xA7. An alternate SFD can be programmed through the SFD register, providing an initial level of

frame filtering for those who choose non-standard compliance. It is a valuable feature when operating in

a congested or private network. The preamble sequence and the SFD are generated by the RADIO, and are

not programmed by the user into the frame buffer.

Following the five octet synchronization header (SHR) is the single octet phy header (PHR). The least

significant seven bits of PHR denote the frame length of the following PSDU. The most significant bit is

reserved and is set to zero for frames that are standard compliant. The RADIO reports all eight bits which

can be used to carry additional information. The PHR is the first byte written to the frame data memory

pointed to by PACKETPTR. Frames with zero length are discarded, and the FRAMESTART event is not

generated in this case.

The next N octets carry the data of the PHY packet, where N equals the value of the PHR. For an

implementation also using the IEEE 802.15.4 MAC layer, the PHY data is a MAC frame of N-2 octets, since

two octets occupy a CRC field.

An IEEE 802.15.4 MAC layer frame consists of the following:

• A header:

• The frame control field (FCF)

• The sequence number

• Addressing fields

• A payload

• The 16-bit frame control sequence (FCS)

MAC protocol data unit (MPDU)

FCF

Frame type

Seq

Addressing fields

MAC payload

FCS

CRC-16

2 octets

Sec

Pend

ACK

Comp

Reserved

Dst A mode

Frame ver

Src A mode

0/4/6/8/10/12/14/16/18/20 octets

Dst PAN ID

Dst address

Src PAN ID

Src address

Security

0/5/6/10/14 octets

MAC header (MHR)

MAC service data unit (MSDU)

(MFR)

Frame control field (FCF) 2 octets

Figure 68: IEEE 802.15.4 frame format (MPDU)

The two FCF octets contain information about the frame type, addressing, and other control flags. This

field is decoded when using the assisted operating modes offered by the RADIO.

The sequence number is a single octet in size and is unique for a frame. It is used in the associated

acknowledgement frame sent upon successful frame reception.

The addressing field can be zero (acknowledgement frame) or up to 20 octets in size. The field is used

to direct packets to the correct recipient and denote its origin. IEEE 802.15.4 bases its addressing on

networks being organized in PANs with 16-bit identifier and nodes having a 16-bit or 64-bit address. In the

assisted receive mode, these parameters are analyzed for address matching and acknowledgement.

The MAC payload carries the data of the next higher layer, or in the case of a MAC command frame,

information used by the MAC layer itself.

4463_156 v1.0

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NRF52820-QDAA-R Datasheet(PDF) 177 Page - Nordic Semiconductor

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