CC2520_11 Datasheet, PDF (70/133 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
19.5 Frame Processing
CC2520 performs the following frame generation tasks for TX frames:
Transmitted frame
Preamble SFD LEN
1
2
MHR
MAC Payload
FCS
3
1. Generation and automatic transmission of the PHY Layer synchronization header which consists of
the preamble and the SFD.
2. Transmission of the number of bytes specified by the frame length field.
3. Calculation of and automatic transmission of the FCS (can be disabled).
The recommended usage is to write the length field followed by MAC header and MAC payload to the TX
FIFO, and let CC2520 handle the rest. Note that the length field must include the two FCS bytes even
though CC2520 adds these automatically.
19.5.1 Synchronization Header
Figure 18: Transmitted Synchronisation Header
CC2520 has programmable preamble length. The default value is compliant with [2] and changing the value
T
T
will make the system non-compliant to IEEE 802.15.4.
The preamble sequence length is set by MDMCTRL0.PREAMBLE_LENGTH. Figure 18 shows how the
CC2520 synchronization header relates to the IEEE 802.15.4 specification.
T
T
When the required number of preamble bytes have been transmitted, CC2520 will automatically transmit the
one byte long SFD. The SFD is fixed and it is not possible to change this value from software.
19.5.2 Frame Length Field
When the SFD has been transmitted, the modulator in CC2520 will start to read data from the TX FIFO. It
expects to find the frame length field followed by MAC header and MAC payload. The frame length field is
used to determine how many bytes that is to be transmitted.
Note that the minimum frame length is 3 when AUTOCRC=’1’ and 1 when AUTOCRC=’0’.
19.5.3 Frame Check Sequence
When the FRMCTRL0.AUTOCRC control bit is set, the FCS field is automatically generated by CC2520 and
appended to the transmitted frame at the position defined by the length field. The FCS is not written to the
TXFIFO, but stored in a separate 16-bit register. It is recommended to always have AUTOCRC enabled,
except possibly for debug purposes. If FRMCTRL0.AUTOCRC=’0’ then the modulator will expect to find the
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