I've had some experience with these Digilent boards, and I'd encourage any potential user to have a VERY careful look at them. I've got nearly every one of the FPGA and CPLD boards they made up to the Spartan3 version, and I've not encountered even one which doesn't have some feature or another that you can "trip over" (excuse the poor grammar, plz).

The Wire Wrap boards are particularly questionable, since they don't provide wire-wrap pins by means of which you can attach to your "system" board.

Issues that have arisen in my experience include the following.

(1) the wire-wrap board is entirely too small. By the time you attach the wire-wrap connectors, for which a site is provided, they leave somewhat less area than a business card, and you have to use a considerable amount of that for electrical terminations, since the unterminated signal at the connectors, swinging typically 3 volts, will have 1.2 volts of over/undershooot and a volt of damped ringing that persists for about 25 ns. You'll want series resistors and schottky diode terminations on each signal you use. (I'd suggest 74S1053 for the 16 terminations in a 20-pin package.) The silkscreen has been wrong for a very long time, and it continues to be wrong, partly for the reason that there's really no "right" way to label both the connectors and the pins. Pin numbers would be OK, I guess, but they'r currently backward from the numbers on their various boards.

I'd recommend buying a "real" wire-wrap board with a 0.100" matrix of plated-through holes and put the appropriate connectors, readily available from Samtec, on it in order to mate with the FPGA board rather than fiddling with the

(2) the "features" included on the "system" board, i.e. the one with the FPGA on it, often interfere with normal "useful" operation of the FPGA. You may not like the way in which the pushbutton is accessible or the way in which it works.

(3) Traces on some of these boards are ridiculously long, owing to their packaging concept. In a couple of the older cases, e.g. the Spartan-2 and -2E boards, there are connectors on diametrically opposite ends of the board that are connected to the same FPGA pins. I don't know what they were thinking this would help, but the signal integrity is TERRIBLE, and possibly worse on the later boards.

Now, these boards are not unuseable, but before using 'em, and they are attractively priced, you should look at the pictures on their web site very closely, read the documentation carefully, study the schematics, and only then decide whether you can make them fit your application.

I'd also point out that many have discussed fitting the XILINX MicroBLAZE core onto one of their boards, using external SDRAM and FLASH, with the goal of running LINUX, but I've never heard of a successful case. It's bound to happen sooner or later, but I've not heard of it yet.

RE