Encoding (8b/10b):
Encoding (64b/66b):
Encryption is for security reason. It has a key, which sender and receiver know.
- to make DC voltage balance by keeping numbers of 1's and 0's equal (using disparity)
- to recov the clock in the receiver by making more transitions in serial data
- to reduce the EMI
- doesn't need scrambling
- transmission overhead is 25% ((2/8)*100)
Encoding (64b/66b):
- just inserts 2 bit preamble to make 64b -> 66b, which acts as bounday comma
- needs scrambling for DC balance, clock recovery at receiver and to reduce EMI
- transmission overhead is 3.125%
Encryption is for security reason. It has a key, which sender and receiver know.
Rapidio and USB 3.0 uses 8b/10b econding but it uses scrambler and descrambling
ReplyDeleteSaravanan,
DeleteThanks, you are right, even the PCI-SIG says same thing on PCI-Express: Along with 8b/10b encoding, Scrambling is also used there. Scrambling is to enhance the DC wander capacity, which is more compared to 8b/10b encoding. But some of the encoded symbols can't be scrambled. This tells that encoding is a must and scrambling is optional.