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AdvaRes
Joined: 14 Feb 2008
Posts: 1038
Helped: 46
Location: At home
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 23 Apr 2008 15:27 serial link+data recovery |
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Hi members,
All we know that CDR is mendatory for receiving Serial Data. In the beginning of a data transfert the tranceiver and the receiver are not synchronized. I need to understand how the receiver can receive correctly the first bits.
Please help.
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Zeinovich314
Joined: 23 Apr 2008
Posts: 1
Helped: 1
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23 Apr 2008 15:38 Re: Clock and data recovery for serial Link |
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in most digital communication techniques, there is some bits sent at first "called preamble" which used to synchronize both Trans. and Receiv.
these preamble bits always 0101010101,,,,and change in size depending on technology type.
example: Ethernet stations need to synchronize with the signal's frequency; this is done by means of 64 preamble bits.
Token-Ring stations are always synchronous to received frames because there is always a signal passing the ring (idle symbols); they only need a 8-bit starting delimiter in order to get ready for receiving the frame.
yours, ZicoŠ
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safwatonline
Joined: 19 Nov 2005
Posts: 1418
Helped: 172
Location: EGYPT
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23 Apr 2008 15:40 Clock and data recovery for serial Link |
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| at first the Rx works on a pll to lock the frequency then uses the received data to capture the correct phase and small frequency errors
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AdvaRes
Joined: 14 Feb 2008
Posts: 1038
Helped: 46
Location: At home
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23 Apr 2008 16:37 Re: Clock and data recovery for serial Link |
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Thanks my friends for your prompts replies.
Concerning the preamble I heared that technique is used for Wireless interconnect. So it is also used in serial link. Thats fine.
But As far as I know, the data is serialized packet by packet (Please correcy me if I'm wrong) and a time space exists between this two serialized data.
My question is, when we plan to send N packets, a preamble is used for each packet (because of the Time space) or only one preamble is used for all the packets (Is the synchronization maintaned in the second case ?).
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23 Apr 2008 16:37 Ads |
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FvM
Joined: 22 Jan 2008
Posts: 5151
Helped: 766
Location: Bochum, Germany
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23 Apr 2008 17:49 Re: Clock and data recovery for serial Link |
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| This looks more like asynchronous transmission. I doesn't need anything but a start bit, if the bit rate is known exactly. Synchronous transmission usually sends an idle frame that's identical to sync frame, e. with HDLC. If you are designing a transmission protocol that hasn't be compatible to any protocol, you can do what you like.
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