External xlink delays

Technical discussions around xCORE processors (e.g. General Purpose (L/G), xCORE-USB, xCORE-Analog, xCORE-XA).
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External xlink delays

Postby Redeye » Tue Dec 04, 2018 9:58 am

I have a board with several external 2-wire xlinks between XL216-TQ128 processors (unfortunately I can't do 5 wire as there aren't enough I/O ports and I can't use BGA devices in this design).

I need these links to run as fast as possible. The tracks are about 10mm long with no damping resistors (yet, though I suspect they may be needed in future). I've run some experiments which ran successfully at a delay in the XN file of 2, but the specs suggest a minimum of 3, if not 4.

Has anyone else run external xlinks at delays of 3 or 4 with success? Or had problems doing so?
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Postby CousinItt » Tue Dec 04, 2018 12:43 pm

You won't need any resistors for such a small distance unless you have problems with RF emissions.

I experimented with two explorer kits side by side and could run a five-way interface reliably below 5 clocks with series termination resistors. In the end I stuck with 5 for peace of mind, since I didn't need to shave off any time.

For guidance on termination see page 12.43 here: https://www.analog.com/media/en/trainin ... pter12.pdf

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