Email: Password: Remember Me | Create Account (Free)

Back to Subject List

Old thread has been locked -- no new posts accepted in this thread
Andy Peters
04/02/10 12:49
Read: 1017 times
Tucson, Az
USA


 
#174787 - deviates
Responding to: Erik Malund's previous message
Erik,

I actually agree with you about experience being a hindrance sometimes.

Here's one that can be baffling. I've done a handful of Xilinx Spartan 3AN designs in the last year, with one Virtex4 design. Now I'm doing a more-complex V4 design and told the layout guy, "You can use any pin that has a _LC or _CC as a differential output but not a differential input because these pins don't have the built-in LVDS termination."

Well, that's the way it is on Spartan 3AN, but that's wrong on V4. V4's "_LC_CC" pins simply don't have differential output drivers. "LC" means "low capacitance" and I guess by eliminating the LVDS output drivers they gain a 1pF improvement in input capacitance, or something. (Oh, and they DO have the built-in 100-ohm LVDS termination.)

So a boatload of LVDS pairs, tuned to matched lengths, had to be reassigned on other pins and rerouted. Yippee!

This is why we never build boards until the FPGA design is done, or at least in a state where all pins and I/O types are well-defined enough to pass through the tools without error or warnings. Especially this board: 14 layers.

-a

List of 65 messages in thread
TopicAuthorDate
Whinge about Eval and Quickstart kits      Oliver Sedlacek      03/19/10 08:10      
   Most time probably spent with other work tasks      Per Westermark      03/19/10 08:17      
   while I basically agree, some comments      Erik Malund      03/19/10 08:24      
      Missing the point (ed)      Andy Neil      03/19/10 08:34      
      What I want..      Oliver Sedlacek      03/19/10 09:32      
         What I want..      Andy Neil      03/19/10 11:48      
            It's a non-starter ... What if I need 5.9908 MHz?      Richard Erlacher      03/26/10 10:30      
               re: What if I need 5.9908 MHz?      Andy Peters      03/26/10 11:12      
                  I think Richard was being generic there...      Andy Neil      03/26/10 11:47      
      Here's what I'd want ...      Richard Erlacher      03/26/10 10:23      
   Unfortunately agree      Andy Neil      03/19/10 08:44      
      Proper documentation is part of the task      Per Westermark      03/19/10 08:54      
         pedagogical      Andy Neil      03/19/10 09:11      
         Fundamental problem with GUIs      Andy Neil      03/19/10 09:16      
            GUI Settings Documentation        Michael Karas      03/19/10 09:36      
               Screenshots      Andy Neil      03/19/10 10:31      
   only today      Jez Smith      03/19/10 10:09      
      That's the reason there's so much junk      Richard Erlacher      03/26/10 16:05      
   as the little girl pointed out...      Jan Waclawek      03/19/10 14:47      
   Previously, on 8052.com...      Andy Neil      03/19/10 16:18      
   who's evaluating who?      James Hinnant      03/20/10 21:09      
   Changing the installation location.      Christoph Franck      03/22/10 02:19      
      filenames with spaces in it      Andy Neil      03/22/10 03:28      
         Exactly      Per Westermark      03/22/10 03:33      
         Bizarre bugs.      Christoph Franck      03/22/10 04:19      
      Spaces      Per Westermark      03/22/10 03:30      
         "My Documents" directory      Andy Neil      03/22/10 03:50      
            May and may...      Per Westermark      03/22/10 05:17      
   Xilinx      Andy Peters      03/23/10 13:06      
      Or, perhaps worse, none ...      Richard Erlacher      03/26/10 16:10      
   What is the purpose?      Andy Neil      03/23/10 17:35      
      The way I see it      Jez Smith      03/24/10 00:20      
         Disagree (mostly)      Andy Neil      03/24/10 00:52      
            well      Jez Smith      03/24/10 01:01      
               quite so      Andy Neil      03/24/10 03:53      
                  Easy to get a customer to move to a competitor      Per Westermark      03/24/10 04:18      
                     The problem stems from...      Jez Smith      03/25/10 01:48      
                        Misses in communication and assumptions alas common      Per Westermark      03/25/10 03:26      
                           'first demo' to a customer ...      Erik Malund      03/25/10 05:42      
                              That's because      Jez Smith      03/25/10 10:53      
               not only that ...      Richard Erlacher      03/26/10 22:34      
         see above ...      Richard Erlacher      03/26/10 22:32      
      I've looked at a lot of "eval" boards ...      Richard Erlacher      03/26/10 22:29      
         app notes      James Hinnant      03/27/10 03:44      
            a CD with their demo boards      Andy Neil      03/27/10 03:47      
            what good would that do?      Erik Malund      03/27/10 05:31      
               mark this on your calendar ... Erik and I agree!      Richard Erlacher      03/27/10 08:39      
               project files      James Hinnant      03/30/10 13:35      
                  how?      Erik Malund      03/30/10 15:02      
                  run != tested      Andy Neil      03/30/10 16:53      
                  That's exactly the wrong attitude      Oliver Sedlacek      03/31/10 03:19      
                     wrong or not, makes sense      Erik Malund      03/31/10 06:09      
                        But      Andy Neil      03/31/10 06:31      
                        What goes around comes around      Per Westermark      03/31/10 06:57      
                           I think something got lost      Erik Malund      03/31/10 07:03      
                              Yes MANUFACTURERS      Per Westermark      03/31/10 07:22      
                                 Per, I do not disagree      Erik Malund      03/31/10 07:27      
                                    no synergy?      Jan Waclawek      03/31/10 08:00      
                                       au contraire      Erik Malund      03/31/10 08:34      
                                       the key is in UNDERSTANDING the example      Richard Erlacher      04/01/10 07:22      
                                    deviate vs derivative      Andy Peters      03/31/10 10:39      
                                       SILabs      Erik Malund      03/31/10 11:30      
                                          deviates      Andy Peters      04/02/10 12:49      
                        Portable within company portfolio      Oliver Sedlacek      03/31/10 08:01      
   Devkits      Andy Neil      03/31/10 15:53      

Back to Subject List