I've inherited a tray of TQFP Spartan-2 (XC2S50, standard performance version) with date code from mid-2001.
Is it worth my while to put these down on prototypes, or have there been significant silicon changes since then/has this family been slated for discontinuation?
If you inherited a box of the "pocket PCs" mid-2001, would you use those in your systems?
If your need is limited to stock on hand and the performance you get from them is sufficient, I'd say "go for it" but if you end up purchasing more of these devices in the long run, you'll probably be MUCH better with a current generation device. The performance is better. The density is significantly greater. The tool support is active rather than legacy. Added functionality is in the new devices. You should expect to be able to get Spartan-IIs for several more years but they are at the bottom of the "price maturity curve" and aren't cost effective compared to new parts.
I just did a quick price compare vs. Spartan-III and I see what you mean. I don't have a specific need for these parts right now; nothing I build uses FPGAs. I was planning to lay down some footprints in "spare" space and wire the FPGA to the footprint of the 8-bit micro I use in an existing design, for experiments. But if I can't be sure of getting these parts on an ongoing basis, there's no point.
The Spartan 2 (XC2S**) are 5 volt tolerant and will easily interface with older 8 bit micros that are 5 volt devices. T he Spartan 2E and later is not 5 volt tolerant. S
With that in mind these parts still have some minimal value.
Whilst FPGA families have an average life of 2 years as the lead family in appropriate sector (low cost sector, or high performance sector), they usually have a very long lifetimes. I wouldn't be surprised if most of the Sparatan-II family are still around in 10 years time going by past history.
For price/performance though it is always hard to beat whatever the latest family is and unless you need the a special feature like 5V tolerance (without resistors or bus switches), or less power supply rails, it is usually worth going to the latest.
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