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Altera_Forum's avatar
Altera_Forum
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14 years ago

Daisy Chain DE2 boards

Hey everyone! First off, I'm new here, so if this is in the wrong section, please move it.

I am attempting to find a way to daisy chain multiple DE2 boards together in order to pass synchronization signals between them (clk, rst, etc). The catch is I can't use the two 40-pin headers for this, because I need those for other purposes. I need to be able to read/control 208 i/o pins on an external daughter board for testing a fab'd IC chip.

I would like to use the USB-A (as input) and USB-B (as output) connectors to do this as this will allow daisy chaining 3 DE2 boards together, thus giving me enough 40-pin connectors across multiple boards for all 208 i/o pins. I've looked through the documentation, but I can not seem to find a way to directly address the 4 pins in the usb connectors. I do not care about usb protocols or standards as these will not be controlling any usb device. Is there any way to simply pass a signal between boards using these ports?

Thanks!

6 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    The DE2 uses the ISP1362 USB Controller, so you would have to talk through that.

    If you want to keep it simple, I would suggest using the RS232. (You could have 2 slaves listening and one master. or buy some rs232->rs485 adapters. Not fast but it works)

    Otherwise, if you have a processor in the EP2C35 anyway, you could always start up the ethernet controller.

    Pete
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    How would I go about having two RS232 slaves? I also forgot to mention that we are shooting for a 50MHz clock, so whatever I use must be able to transmit that signal. Thanks for your reply!

  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    The simplest way, is just cut the TX line from the second slave, and have a protocol that doesn't require acks or responses. But you can use an RS232-RS484 converter, and then address each slave to respond. (With a serial protocol)

    The issue is your max speed at RS232 is going to be around 1 Mbps. and it's serial, so you divide the number by 10 to get your throughput. It's fine if all you are doing is sending commands, but if you are trying to push a bunch of data between the boards, I think you'll be stuck.

    You can find RS232 to RS485/422 converts at lots of places, including Amazon.com.. (just do a quick search). It's basically similar to RS232, but is meant as a multi-drop system. So you can have more than two devices on the bus. RS485 vs RS422 is just Half Duplex-vs-Full Duplex.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Quite honestly, distributing clocks and resets through the RS-232 transceivers looks like a bad idea.

    The DE2 has a external clock input, using a SMA connector. I suggest you use that one for distributing clock to all 3 DE2 boards.

    Then work into fitting your remaining needs into the 40 pin headers.

    Ie, I suggest you put a debounced push button on your daughter card to generate the RESET and feed it back to the DE2 boards though a pin in one of the 40 pin headers.
  • Altera_Forum's avatar
    Altera_Forum
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    14 years ago

    Yeah, that's definitely a better idea. Sometimes I get so wrapped up in my first plan, the simple, elegant solutions slip right by. Thanks a ton.