Wel, Jan, my first experience with what later became XILINX' 2000 series was via MMI, which not only developed the early PAL families, but had FPGA's in their arsenal as well.

The labels on my early XACT software and my early PALASM software are both MMI, as are the databooks.

Another way to look at the various FPGA architectures is to consider them as being little more than RAM with feedback. PLD's can be looked upon as being macrocell arrays, as in PALs and CPLD are simply complex arrays of them, with various and complex interconnection schemes.

From a practical standpoint, I'd point out that, if you have a schematic, and enter it into your choice of programmable logic design tools, you're more likely to succeed in integrating what's in your discrete SSI/MSI design using a CPLD than an FPGA, though either is possible.

Somebody pointed out that CPLD's are commonly used as glue logic. That's true, particularly since SSI/MSI blocks are becoming scarcer, and CPLD's are becoming cheaper.

As for the cost matter, I'd encourage those who are interested to consult eBay for JTAG-programmable logic and for the gadgets with which to program 'em. You can, of course, build a simple JTAG programmer if you follow the recipe provided by nearly any/all of the device vendors. Note, however, that you'll have to build one specific to each manufacturer, since they insist on slight differences so as to keep those unwilling to "roll-yer-own" multiple times from moving between vendors. I've routinely bought 32 or 36 macrocell CPLD's for a buck or so and 128 macrocell CPLDs for $2. Some people insist on paying upward of $10. A look in the DigiKey catalog would cure the sensible ones of that, but sometimes it's testosterone rather than good sense that motivates buyers on eBay. I don't recommend buying parts that you can't immediately erase, program, or otherwise check out. The first one might be an exception, but BEWARE ... not all devices are eraseable.

RE