Manchester encoding, self clocking question

Thread Starter

bug13

Joined Feb 13, 2012
1,864
Hi team

How manchester self clock? refer to image, how does it tell where the two GREEN ARROW is not ZERO?

650px-Manchester_encoding_both_conventions.svg.png
 

MrChips

Joined Oct 2, 2009
21,890
Manchester encoding is also known as phase-encoded.
The direction of the transition tells you if the data is 0 or 1.

Take a look at the bottom trace.
A rising edge identifies a 1.
A falling edge identifies a 0.

After that, you have to ignore any transitions that occur before a half bit width has expired, i.e. ignore the transitions you have indicated with the green arrows.
 

Thread Starter

bug13

Joined Feb 13, 2012
1,864
Thanks guys @nsaspook and @MrChips

So referring to the image below, if I am at the receiving end, how can I tell the data is 1 1 1, but not 10101?? How can I tell how much time is one bit?

PS: Assuming the receiver don't know how many bit the transceiver are sending.

1200px-Manchester_encoding_both_conventions.svg.png
 

Thread Starter

bug13

Joined Feb 13, 2012
1,864
Just an thought,

Does it normally send a known data stream first? Say send 32 bits of 1s to synchronize the signal so the receiver can work out the data rate?
 

MrChips

Joined Oct 2, 2009
21,890
You need to know the bit width (approximate).

Yes, you need to send a synchronizing byte. Any byte that begins with 10xxxxxx will do.
If you send 10101010, the receiver can figure out the bit width.
 

MrChips

Joined Oct 2, 2009
21,890
What I wrote with regards to the bit order can be misleading.
If the LSB is transmitted first then you want the synchronizing byte to be xxxxxx01.
 
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