CC2520_11 Datasheet, PDF (101/133 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
27 Packet Sniffing
Packet sniffing is a non-intrusive way of observing data that is either being transmitted or received by
CC2520. The packet sniffer outputs a clock and a data signal which should be sampled on the rising edges
of the clock. The two packet sniffer signals are observable as GPIO outputs. For accurate time stamping,
the SFD signal should also be output.
Because CC2520 only supports a data rate of 250kbps, the packet sniffer clock frequency is 250 kHz. The
data is output serially with the MSB of each byte first, which is opposite of the actual RF transmission, but
more convenient when processing the data. It is possible to use an SPI slave to receive the data stream.
When sniffing frames in TX mode, the data that is read from the TX FIFO by the modulator is the same data
that is output by the packet sniffer. However, if automatic CRC generation is enabled, the packet sniffer will
NOT output these 2 bytes. Instead, it will replace the CRC bytes with 0x8080. This value can never occur as
the last two bytes of a received frame (when automatic CRC checking is enabled), and thus it provides a
way for the receiver of the sniffed data to separate frames that were transmitted by the CC2520 and frames
that were received by the CC2520.
When sniffing frames in RX mode, the data that is written to the RX FIFO by the demodulator is the same
data that is output by the packet sniffer. In other words, the last two bytes are either the received CRC value
or the CRC OK/RSSI/correlation/SRCRESINDEX value that may automatically replace the CRC value,
depending on configuration settings.
Note that in order to observe the packet sniffing data on GPIO pins, the packet sniffer module must be
enabled in the MDMTEST1 register, and the correct GPIO configuration must be written to any of the GPIOn
registers.
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