Link 'buffer' question

Technical discussions around xCORE processors (e.g. General Purpose (L/G), xCORE-USB, xCORE-Analog, xCORE-XA).
vanjast
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Link 'buffer' question

Post by vanjast »

A question for those who have made their own pcb's

Has anyone buffered their Link lines across different pcbs.
If not, are the Links 'stable' through connectors (say IDC) ?

I'm thinking that I should use some LVDS buffers for the links, which is an extra hassle, but If this is not necessary, I'd prefer to go without this.

Thanks
Van


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TonyD
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Post by TonyD »

The XK-1 boards use a standard 20-pin IDC headers to interconnect to other XK-1 boards so I wouldn't have thought it a problem unless you're planning on having your boards some distance away from each other.
vanjast
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Post by vanjast »

Ja.. I'm just worried about the impedance matching, even at short distances across IDC.
I haven't done this thing before, so I'm 'treading carefully'.

I'll have to settle for LVDS as I do not want to restrict myself to short distances.
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Bianco
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Post by Bianco »

Xlinks over LVDS has been done succesfully
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dan
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Post by dan »

Hi Vanjast,

you should find these new app notes useful in answering your questions.

xmos.com->Support->Documentation: Silicon

XS1-L Link Performance/Design Guidelines
XS1-G Link Performance/Design Guideline

Not sure whether you are using XS1-L or G.

Let me know if these notes answer your questions.

Cheers,

Dan
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lilltroll
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Post by lilltroll »

In the XMOS video with Dave and the thin ribbon-cable to interconnect L1's, they use a buffer for the 5pin interface.
Probably not the most confused programmer anymore on the XCORE forum.
vanjast
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Post by vanjast »

Just got back from a trip...
Thanks for the further replies.. I'll have a look at these
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Woody
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Post by Woody »

I've been using unbuffered links down IDC cable lengths of 20cm or so with good data rates.

If you need integrity at the expense of link performance you can always slow the links down by using a large delay between the links (inter-symbol delay). That way you can transfer data across really quite poor links. Each symbol corresponds to a transition on one of the link wires. So long as each symbol being transmitted is received as a single symbol (i.e. a transition is not received as 3 transitions due to ringing etc) the link's integrity should be fine.