Single-Chip Low Cost Low Power RF-Transceiver (Rev. A)

CC2500Figure 10: Data whitening in TX mode15.2 Packet FormatThe format of the data packet can beconfigured and consists of the following items(see Figure 11):• Preamble• Synchronization word• Length byte or constant programmablepacket length• Optional address byte• Payload• Optional 2 byte CRCOptional data whiteningOptionally FEC encoded/decodedOptional CRC-16 calculationLegend:Inserted automatically in TX,processed and removed in RX.Preamble bits(1010...1010)Sync word8 x n bits 16/32 bitsLength field8bitsAddress field8bitsData fieldCRC-168 x n bits 16 bitsFigure 11: Packet formatOptional user-provided fields processed in TX,processed but not removed in RX.Unprocessed user data (apart from FECand/or whitening)The preamble pattern is an alternatingsequence of ones and zeros (01010101…).The minimum length of the preamble isprogrammable. When enabling TX, themodulator will start transmitting the preamble.When the programmed number of preamblebytes has been transmitted, the modulator willsend the sync word and then data from the TXFIFO if data is available. If the TX FIFO isempty, the modulator will continue to sendpreamble bytes until the first byte is written tothe TX FIFO. The modulator will then send thesync word and then the data bytes. Thenumber of preamble bytes is programmed withthe MDMCFG1.NUM_PREAMBLE value.The synchronization word is a two-byte valueset in the SYNC1 and SYNC0 registers. Thesync word provides byte synchronization of theincoming packet. A one-byte sync word can beemulated by setting the SYNC1 value to thepreamble pattern. It is also possible to emulatea 32 bit sync word by usingMDMCFG2.SYNC_MODE=3 or 7. The sync wordwill then be repeated twice.CC2500 supports both fixed packet lengthprotocols and variable packet length protocols.Variable or fixed packet length mode can beused for packets up to 255 bytes. For longerpackets, infinite packet length mode must beused.PRELIMINARY Data Sheet (Rev.1.2) SWRS040A Page 27 of 83