Single-Chip Low Cost Low Power RF-Transceiver (Rev. B

CC250015.1 Data WhiteningFrom a radio perspective, the ideal over the airdata are random and DC free. This results inthe smoothest power distribution over theoccupied bandwidth. This also gives theregulation loops in the receiver uniformoperation conditions (no data dependencies).Real world data often contain long sequencesof zeros and ones. Performance can then beimproved by whitening the data beforetransmitting, and de-whitening the data in thereceiver. With CC2500, this can be doneautomatically by settingPKTCTRL0.WHITE_DATA=1. All data, exceptthe preamble and the sync word, are thenXOR-ed with a 9-bit pseudo-random (PN9)sequence before being transmitted as shownin Figure 10. At the receiver end, the data areXOR-ed with the same pseudo-randomsequence. This way, the whitening is reversed,and the original data appear in the receiver.The PN9 sequence is reset to all 1’s.Data whitening can only be used whenPKTCTRL0.CC2400_EN=0 (default).Figure 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)SWRS040B Page 30 of 92