Texas Instruments 3138 155 232931 - Manual (Page 41)

CC2420
SWRS041B Page 41 of 89
18 Address Recognition
CC2420 includes hardware support for
address recognition, as specified in [1].
Hardware address recognition may be
enabled / disabled using the
MDMCTRL0.ADR_DECODE
control bit.
Address recognition is based on the
following requirements, listed from section
7.5.6.2 in [1]:
• The frame type subfield shall not
contain an illegal frame type
• If the frame type indicates that the
frame is a beacon frame, the
source PAN identifier shall match
macPANId unless macPANId is
equal to 0xFFFF, in which case
the beacon frame shall be
accepted regardless of the source
PAN identifier.
• If a destination PAN identifier is
included in the frame, it shall
match macPANId or shall be the
broadcast PAN identifier
(0xFFFF).
• If a short destination address is
included in the frame, it shall
match either macShortAddress or
the broadcast address (0xFFFF).
Otherwise if an extended
destination address is included in
the frame, it shall match
aExtendedAddress.
• If only source addressing fields
are included in a data or MAC
command frame, the frame shall
only be accepted if the device is a
PAN coordinator and the source
PAN identifier matches
macPANId.
If any of the above requirements are not
satisfied and address recognition is
enabled,
CC2420 will disregard the
incoming frame and flush the data from
the RXFIFO. Only data from the rejected
frame is flushed, data from previously
accepted frames may still be in the
RXFIFO.
The IOCFG0.BCN_ACCEPT control bit
must be set when the PAN identifier
programmed into
CC2420 RAM is equal to
0xFFFF and cleared otherwise. This
particularly applies to active and passive
scans as defined by [1], which requires all
received beacons to be processed by the
MAC sublayer.
Incoming frames with reserved frame
types (FCF frame type subfield is 4, 5, 6 or
7) is however accepted if the
RESERVED_FRAME_MODE
control bit in
MDMCTRL0
is set. In this case, no further
address recognition is performed on these
frames. This option is included for future
expansions of the IEEE 802.15.4
standard.
If a frame is rejected, CC2420 will only start
searching for a new frame after the
rejected frame has been completely
received (as defined by the length field) to
avoid detecting false SFDs within the
frame.
The
MDMCTRL0.PAN_COORDINATOR
control bit must be correctly set, since
parts of the address recognition procedure
requires knowledge about whether the
current device is a PAN coordinator or not.
19 Acknowledge Frames
CC2420 includes hardware support for
transmitting acknowledge frames, as
specified in [1]. Figure 23 shows the
format of the acknowledge frame.
If MDMCTRL0.AUTOACK is enabled, an
acknowledge frame is transmitted for all
incoming frames accepted by the address
recognition with the acknowledge request
flag set and a valid CRC. AUTOACK
therefore does not make sense unless
also ADR_DECODE and AUTOCRC are
enabled. The sequence number is copied
from the incoming frame.