CC2520_11 Datasheet, PDF (71/133 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
FCS in the TX FIFO, so software must generate the FCS and write it to the TX FIFO along with the rest of
the MPDU.
The CC2520 hardware implementation of the FCS calculator is shown in Figure 22. Please refer to [2] for
T
T
further details.
Figure 19: CC2520 FCS hardware implementation
19.6 Exceptions
The SFD exception will be raised when the SFD field of the frame has been transmitted. At the end of the
frame, the TX_FRM_DONE exception will be raised when the complete frame has been successfully
transmitted.
Note that there is a second SFD signal available on GPIO (config value 0x2A) that should not be confused
with the SFD exception.
19.7 Clear Channel Assessment
The clear channel assessment (CCA) status signal indicates whether the channel is available for
transmission or not. The CCA function is used to implement the CSMA-CA functionality specified in the
IEEE 802.15.4 specification [2]. The CCA signal is valid when the receiver has been enabled for at least 8
symbol periods. The RSSI_VALID status signal can be used to verify this.
The CCA is based on the RSSI value and a programmable threshold. The exact behavior is configurable in
the CCACTRL0 and CCACTRL1 registers.
There are two variations of the CCA signal, one that is updated at every new RSSI sample and one that is
only updated on SSAMPLECCA and STXONCCA command strobes. They are both available in the
FSMSTAT1 register.
Note that the CCA signal is updated 4 clock cycles (32 MHz) after the RSSI_VALID signal has been set.
19.8 Output Power Programming
The RF output power of CC2520 is controlled by the 7 bit value in the TXPOWER register. Table 17 shows
the typical output power and current consumption for the recommended settings when the centre frequency
is set to 2440 GHz. Note that the recommended settings are only a small subset of all the possible register
settings. Using other settings than those in Table 17 might result in very high current consumption and
generally poor performance. Please refer to section 5.11 for details on the optional temperature
compensated TX.
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