14.3.1.2.2 Frame Control Field (FCF)

The FCF consists of 16 bits, and occupies the first two octets of the MPDU or PSDU, respectively.

Bits [2:0]: describes the “Frame Type“. The table below summarizes frame types defined by IEEE 802.15.4-2006 [2], Section 7.2.1.1.1.

This subfield is used for frame filtering by the third level filter rules. By default, only frame types 0 – 3 pass the third level filter rules, refer to Section 8.2. Automatic frame filtering by the AT86RF212B is enabled when using the RX_AACK mode.

However, a reserved frame (frame type value > 3) can be received if the AACK_UPLD_RES_FT bit in the XAH_CTRL_1 register (XAH_CTRL_1.AACK_UPLD_RES_FT) is set.

Frame filtering is also provided in Basic Operating Mode.

Bit 3: indicates whether security processing applies to this frame. This field is evaluated by the Frame Filter.

Bit 4: is the “Frame Pending” subfield. This field can be set in an acknowledgment frame (ACK) in response to a data request MAC command frame. This bit indicates that the node, which transmitted the ACK, might have more data to send to the node receiving the ACK.

Bit 5: forms the “Acknowledgment Request” subfield. If this bit is set within a data or MAC command frame that is not broadcast, the recipient shall acknowledge the reception of the frame within the time specified by IEEE 802.15.4, that is within 12 symbol periods for nonbeacon-enabled networks.

The radio transceiver parses this bit during RX_AACK mode and transmits an acknowledgment frame if necessary.

In TX_ARET mode this bit indicates if an acknowledgement frame is expected after transmitting a frame. If this is the case, the receiver waits for the acknowledgment frame, otherwise the TX_ARET transaction is finished.

Bit 6: the “PAN ID Compression” subfield, indicates that in a frame where both the destination and source addresses are present, the PAN ID is omitted from the source addressing field. This bit is evaluated by the Frame Filter of the AT86RF212B. This subfield was previously named “Intra-PAN”.

Bits [11:10]: the “Destination Addressing Mode” subfield describes the format of the destination address of the frame. The values of the address modes are summarized in the table below, according to IEEE 802.15.4.

If the destination address mode is either two or three (that is if the destination address is present), it always consists of a 16-bit PAN-ID first, followed by either the 16-bit or 64-bit address as described by the mode.

Bits [13:12]: the “Frame Version” subfield specifies the version number corresponding to the frame. These bits are reserved in IEEE 802.15.4-2003.

This subfield shall be set to zero to indicate a frame compatible with IEEE 802.15.4‑2003 and one to indicate an IEEE 802.15.4-2006 frame All other subfield values shall be reserved for future use.

The AACK_FVN_MODE bit in the CSMA_SEED_1 register (CSMA_SEED_1.AACK_FVN_MODE) controls the behavior of frame acknowledgements. This register determines if, depending on the Frame Version Number, a frame is acknowledged or not. This is necessary for backward compatibility to IEEE 802.15.4-2003 and for future use. Even if frame version numbers two and three are reserved, it can be handled by the radio transceiver.

Bits [15:14]: the “Source Addressing Mode” subfield, with similar meaning as “Destination Addressing Mode”.

The addressing field description bits of the FCF (Bits 0–2, 3, 6, 10–15) affect the AT86RF212B Frame Filter.