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

Postby vanjast » Fri Feb 05, 2010 9:04 pm

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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Postby TonyD » Sun Feb 07, 2010 9:13 pm

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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Postby vanjast » Tue Feb 09, 2010 10:12 pm

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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Postby Bianco » Thu Feb 18, 2010 3:46 pm

Xlinks over LVDS has been done succesfully
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dan
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Postby dan » Tue Feb 23, 2010 5:52 pm

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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Postby lilltroll » Tue Feb 23, 2010 6:37 pm

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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Postby vanjast » Sat Mar 06, 2010 12:08 pm

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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Postby Woody » Mon Mar 08, 2010 10:15 am

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.

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