Jeff Epler wrote: > On Mon, Aug 25, 2008 at 09:01:27PM -0500, Jon Elson wrote: > >>This is the parallel port (EPP) version. > > > With at least a few systems, the problem goes deeper than this: the FPGA > firmware is programmed each time over the parallel-port in SPP mode. > One machine we had at CNC Workshop wouldn't even complete this step > successfully with the example "blink the LED" FPGA firmware. Yes, I saw you struggling with it there. The problem is these FPGAs are very fast, and a 1 or 2 ns bounce on the config clock or JTAG clock line could be interpreted as two clocks. They assume that you are filtering whatever signals you are sending to the FPGA or that they are being sent from a microprocessor a few inches away, not from a long cable. I know that downloading Xilinx FPGAs and even CPLDs using the parallel port can be a problem, and some motherboards just don't work. Open up a Xilinx DLC5 (Parallel Cable III) or look up the schematic on their web site to see some of the filtering junk they need to do. An IEEE-1284 cable should be better than the usual printer cable, at least for the strobe lines, but they STILL suffer from a lot of crosstalk. I have built some custom gadgets at work that use IEEE-1284 over 30+ foot cables. I made my own cables out of twisted-pair ribbon cable, with a separate pair for each signal, including all the data lines. This works flawlessly.
I'd be willing to bet a meal at the next Workshop that this is either a crosstalk or reflection problem on whatever signal is used to clock the config data into the FPGA. A custom cable, or just pluging the board right into the par port connector on the computer might prove it, although that doesn't FIX the problem in a practical way. It may need RC filters and a Schmitt trigger on the board to really fix it. Jon ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
