Interconnect over CAT-5/6 cable

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SpacedCowboy
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Interconnect over CAT-5/6 cable

Post by SpacedCowboy »

Hey guys,

So I'm wanting to use a couple of XMOS chips to implement a low-latency reasonable-bandwidth link between a computer system and a bus-expansion for said computer system. Basically I don't want a 40-way IDC cable between the two so the goal is to use a 2-way link.

So, assuming:
  • I use Cat5/Cat5e/Cat6 wiring - is there likely to be any difference, btw ?
  • I use differential signaling (eg: DS90LV049TMTX)
  • I implement some transport-level error checking (similar to AN01024)
  • I keep the network cable reasonably short (a couple of meters, tops)
... I'm hoping this is likely to work. Now onto the question:

Is there a tried-and-tested circuit anywhere ? I can't find one if so. I'm not sure if I ought to be putting series resistors into the uplink path (similar to the XTAG interface). I see there is a board being used by XMOS (figure 4 in AN01024) and those boards definitely look as though they have more than just a straight-through connection...

Is it possible to get hold of the circuit diagram for the board in the application-note ?


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mon2
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Post by mon2 »

We did the following design and PCB layout under p/n LF1071KB. The design has been on freeze due to limited spare time. We do have the bare PCBs and raw materials in house but not moved to first assembly for testing:

http://www.xcore.com/viewtopic.php?f=44 ... 1KB#p28571

Schematics are posted inside the referenced download.
SpacedCowboy
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Post by SpacedCowboy »

Thanks! That's *really* useful :)

One question: It looks from the schematic that you're using 2 RJ45 connectors per link, is that because you wanted the auto-detect of cross-over cable or not ? Or is it because of signal integrity concerns ?

If it comes down to whether to support x-over or only need 1 cable, I'm definitely coming down on the side of 1 cable. This isn't for commercial distribution or anything like that, those that I do give it to, I can give a known-good working cable as well :)

It looks as though you're providing 2 link transports as well (presumably because you could :) - I'll just cut that down to 1 link for my purposes :)

Thanks again!
Simon
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mon2
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Post by mon2 »

Hello Simon. Thanks for the kind comments. Been a while but from memory, we did want to support the ability to auto-detect the cable wiring that will be used between the links AND also support 5 wire differential signals for higher throughput vs. 2 wire (respectively, lower throughput). Again from memory, we noted that there are 2 different wiring specs for the CAT5 / CAT6 cables (CAT6 is preferred for the small premium and guaranteed signal quality) - straight through and cross wire. There are some public charts that offer the exact pinout and can review once back to the office on Monday but regardless, the circuit was drawn so that the proper signal land automatically on the other side of the cable.

We brought in a special 2 x 2 RJ45 stacked connector combo out of Shenzhen China (supplier: Link-PP). Will share more info once we can find the entire project fileset.

p/n LPJE1073AHNL

Summary: More RJ45 connection = 5 wire support with auto-routing of the signals using off-the-shelf patch cables (fully-loaded).
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