CC2520_15 Datasheet, PDF (76/134 Pages) Texas Instruments – 2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER

CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
If a frame is rejected, CC2520 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. Note that
rejected frames can generate RX overflow if it occurs before the frame is rejected.
Exceptions
When frame filtering is enabled and the filtering algorithm accepts a received frame, an
RX_FRM_ACCEPTED exception will be generated. It will not be generated if frame filtering is disabled or
RX_OVERFLOW or RX_FRM_ABORTED is generated before the filtering result is known.
Figure 24 illustrates the three different scenarios (not including the overflow and abort error conditions).
Figure 21: Filtering scenarios (exceptions generated during reception)
The FSMSTAT1.SFD register bit will go high when start of frame delimiter is completely received and
remain high until either the last byte in MPDU is received or the received frame has failed to pass address
recognition and been rejected.
SFD exception can be routed to a GPIO pin alone or as a part of a group of exceptions in channel A or B.
SFD exception should preferably be connected to a timer capture pin on the microcontroller to extract timing
information of transmitted and received data frames. SFD exception is also stored in EXCFLAG1 register.
The register bit (and possibly the GPIO pin) will go high when the start of frame delimiter has been
completely received and will continue to be high until cleared by SW.
Tips and Tricks
The following register settings must be configured correctly:
• FRMFILT0.PAN_COORDINATOR must be set if the device is a PAN coordinator, and cleared if not.
• FRMFILT0.MAX_FRAME_VERSION must correspond to the supported version(s) of the IEEE
802.15.4 standard.
• The local address information must be loaded into RAM.
To completely avoid receiving frames during energy detection scanning, set FRMCTRL0.RX_MODE = 0b11
and then (re)start RX. This will disable symbol search and thereby prevent SFD detection.
To resume normal RX mode, set FRMCTRL0.RX_MODE = 0b00 and (re)start RX.
During operation in a busy IEEE 802.15.4 environment, CC2520 will receive large numbers of non-intended
acknowledgment frames. To effectively block reception of these frames, use the
FRMFILT1.ACCEPT_FT2_ACK bit to control when acknowledgment frames should be received:
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