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It is a description of PHY package format of a power line communicaiton protocal.
As figure6.11, each byte in NPDU has 1 parity bit on Bit9, and fixed "0" and "1" on Bit10 and 11. However, the shole package has 2 bytes CRC16 bytes at the end of the package.
Now please, why the bit parities is needed since the CRC16 can make sure the correct of all the data? whe the receiver find that the parity bit is not correct when it is receiving, should it quit the next receiving action?
Because maybe the error bit is only the parity bit itself, so I don't think quit receiving is wise. But, if the crc is the final judgement of the validity of the package, the parity bit is nonsese. So why?
p.s. what is the useage of the fixed "01" bits? symbol timing recovery? if the sampling and judgement of the receiver is not "01", what should PHY receiver do?
Thanks a lot!