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Visitor wmeyer
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Registered: ‎08-02-2019

Connect 2 AC701 boards via FMC HPC

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In developing an Artix7-to-Artix7 application, I presumed I could use the FMC HPC connectors on 2 AC701 boards connected with an FMC HPC cable to support board-to-board coms.  Turns out this configuration shorts the JTAG TDI/TDO of both boards, rendering the boards deaf.  Is there an off-the-shelf cable out there that allows such a board-to-board connection?  Is there a jumper on the AC701 board that would facilitate this board-to-board comms?

Thanks in advance

 

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Visitor wmeyer
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Registered: ‎08-02-2019

Re: Connect 2 AC701 boards via FMC HPC

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Solution found!  Invested in a pair of Xillinx FMC-105-DEBUG mezzanine cards and a ribbon cable.  This enabled my app to run AC701 to AC701 comms, connecting only the signals of interest between the two AC701 boards.  Each FMC-105 card needed a jumper connecting TDI & TDO to maintain JTAG access from the host PC.  Overall, a fairly simple solution, with the benefit that all FMC signals are available on the FMC-105 card for debug/probe.

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Registered: ‎01-22-2015

Re: Connect 2 AC701 boards via FMC HPC

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@wmeyer 

The following figure from page 4 of the AC701 schematic shows what's happening.
AC701_JTAG.jpgWhen the FMC cable is connected then switch, U27, opens and you’ve lost the normal JTAG TDI connection.  Worse than that, you’ve got the TDI lines from both AC701 boards battling.   Somehow, you need to break the two TDI connections to the FMC connector (or carefully cut two wires in the FMC cable) and keep switch, U27, closed.    -not easy to do, I'm afraid.

Mark

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Visitor wmeyer
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Registered: ‎08-02-2019

Re: Connect 2 AC701 boards via FMC HPC

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@markg- thanks for the pointer.  You nailed the same issue I referenced, but I found it a bit more subtle.  From p. 24 of the AC701 schematic:

AC701-p24-U27.PNG

The net FMC1_HPC_PRSNT_M2C_B controls the switch U27 state.  This net is driven from pin N16 of the Artix7, and defaults to 1 with an external pull-up if pin N16 is undriven.  The net also connects to pin H2 of the FMC HPC connector, which effectively hard-wire ANDs the Artix7 pin N16 of both AC701 boards - either N16 driven LO will open both boards' switch U27.  The battling JTAG signals occurs even when switch U27 remains closed, since the cable connects both boards' JTAG TDI/TDO signals.

The cable I have is a Hitech Global FMC-TO-FMC. I now appreciate that this cable is intended for connecting a mezzanine card to the AC701 via FMC HPC, and not for connecting 2 AC701 boards.  My soultion is starting to look like a custom cable.

I was hoping to hear that someone had already been down this path and found a solution ... apparently not the case.

 

 

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Moderator
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Registered: ‎06-14-2010

Re: Connect 2 AC701 boards via FMC HPC

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Hello @wmeyer ,

Is there any further assistance required in relation to this matter? If so, please let us know and we will be glad to help you further then.

However if your query is answered now, please mark a response as 'Accepted Solution' (more info on this can be found here: https://forums.xilinx.com/t5/help/faqpage/faq-category-id/solutions#solutions), so that the topic can be completed then.

We appreciate your help.

Kind Regards,
Anatoli Curran,
Xilinx Technical Support
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Visitor wmeyer
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Registered: ‎08-02-2019

Re: Connect 2 AC701 boards via FMC HPC

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Solution found!  Invested in a pair of Xillinx FMC-105-DEBUG mezzanine cards and a ribbon cable.  This enabled my app to run AC701 to AC701 comms, connecting only the signals of interest between the two AC701 boards.  Each FMC-105 card needed a jumper connecting TDI & TDO to maintain JTAG access from the host PC.  Overall, a fairly simple solution, with the benefit that all FMC signals are available on the FMC-105 card for debug/probe.

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