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Question: What is the purpose of the Start of Packet (SOP) codes in WirelessUSB LP systems?
Start of packet (SOP) symbols are used to bound the beginning of the packet data, and also provide the added feature of encoding the data rate for the remainder of the packet. SOP is composed primarily of two symbols. Each symbol is either a 32-chip or 64-chip PN code. WirelessUSB LP family devices correlate packets based upon SOP PN codes when enabled. What this means is that if a receiver successfully correlates on an SOP, then the receive state machine will run to completion and will receive a packet, regardless of the validity of the remainder of the data. Failing to correlate on an SOP results in no packet being received even if valid data follows. SOP is enabled or disabled with bit 7, SOP EN, of the FRAMING_CFG_ADR register 0x10. The length, 32 chip or 64 chip, is set using bit 6, SOP LEN, of the FRAMING_CFG_ADR register 0x10. The SOP code itself is stored in the SOP_CODE_ADR file register 0x22, which consists of eight bytes.