CC2520_11 Datasheet, PDF (74/133 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
1. Detection and removal of the received PHY synchronization header (preamble and SFD), and
reception of the number of bytes specified by the frame length field.
2. Frame filtering as specified by [1] and [2], section 7.5.6.2, third filtering level.
3. Matching of the source address against a table containing up to 24 short addresses or 12 extended
IEEE addresses. The source address table is stored on-chip in RAM.
4. Automatic FCS checking, and attaching this result and other status values (RSSI, LQI and source
match result) to received frames.
5. Automatic acknowledgment transmission with correct timing, and correct setting of the frame
pending bit, based on the results from source address matching and FCS checking.
20.3.1 Synchronization Header And Frame Length Fields
Frame reception starts with detection of a start-of-frame delimiter (SFD), followed by the length byte, which
determines when the reception is complete. The SFD signal, which is default output on GPIO4, can be
connected to a timer input on a microcontroller to capture the start of received frames:
Figure 20: SFD signal timing
Preample and SFD are not written to the RX FIFO.
The CC2520 uses a correlator to detect the SFD. The correlation threshold value in
MDMCTRL1.CORR_THR determines how closely the received SFD must match an "ideal" SFD. The
threshold must be adjusted with care:
• If set too high, CC2520 will miss lots of actual SFDs, effectively reducing the receiver sensitivity.
• If set too low, CC2520 will detect lots of false SFDs. Although this does not reduce the receiver
sensitivity, the effect will be similar, since false frames might overlap with SFDs of actual frames. It also
increases the risk of receiving false frames with correct FCS.
In addition to SFD detection, it is also possible to require a number of valid preamble symbols (also above
the correlation threshold) prior to SFD detection. Refer to the register descriptions of MDMCTRL0 and
MDMCTRL1 for available options and recommended settings.
For CC2520 rev. A the default correlation threshold is too low, and must updated after reset (before RX is
attempted).
20.3.2 Frame Filtering
The frame filtering function rejects non-intended frames as specified by [1] and [2], section 7.5.6.2, third
filtering level. In addition, it provides filtering on:
• The 8 different frame types (see the FRMFILT1 register)
• The reserved bits in the frame control field (FCF)
The function is controlled by:
• The FRMFILT0 and FRMFILT1 registers
• The LOCAL_PAN_ID, LOCAL_SHORT_ADDR and LOCAL_EXT_ADDR values in RAM
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