Re: Very low pin count FPGA

Both the Coolrunner II and the 9500 series are very limited in capability a nd in the case of the Coolrunner II can be rather expensive for the larger devices. They also only package the smallest devices in the smallest packa ges. They just aren't useful for much other than simple CPLD type applicat ions. Maybe that's because they are simple CPLDs?

Rick C.

Well, the OP did say he had ONE input and ONE output (plus clock) so that seems like it could be a pretty small circuit. I have a case where I needed 3 sequential reset pulses to put an Analog Devices chip in the proper state upon power-up. The smallest XC9536 (now upgraded to XC9536XL) was perfect, and smaller than I could have done it with 2

Since the OP didn't give much info, I had to make assumptions on how much logic he needed.

Jon

Yeah, but if you are still working on the OPs needs he said he wanted a dev ice in an "SOIC-8 or similar".

That is the crux of the problem. There are some number of applications whi ch require more logic than a 22V10 but in a similar size package. Just as there is a wide range of MCU sizes in capability and packages it would be u seful to have a similar range of capacities and packages for FPGAs. Not al l MCUs in a 20 pin package are limited to 8 kB of Flash, some go well beyon d that. But in FPGAs they seem to be less interested in a proliferation of die types so when they plan their devices a die with this must logic has t his many I/O pins and they try to make as many as possible in the packages.

I was once told the die sizes in low end FPGAs are I/O bound. So the highe r pin counts become a self fulfilling prophesy so they can charge more. I' ve also been told the FPGA makers have no interest in competing in the same application space as MCUs since the margins are much narrower. The big tw o FPGA makers are in the same mindset that their primary market is to suppl y the larger devices to the large communications vendors. Everything else is picking up bread crumbs.

If it weren't for that FPGAs would support many of the same interfaces that MCUs do and be available in similar packaging - able to compete head to he ad for applications that don't take a quarter MB of program to implement. Lattice presently has a 384 LUT device for just a couple of bucks, but it i s in a package with 0.4 mm ball pitch which is not so easy to work with wit hout a very fine PWB process and micro vias.

Rick C.

Yup, that makes the problem harder. Really, the 44-pin QFP isn't a WHOLE bunch bigger than an SOIC-8. And, maybe there are some devices I don't know about that are in such a small package.

Jon

I've never seen anything in an 8 pin package, not even a PLD. There are co mpanies that make "programmable" logic in very pin limited packages. But t hey aren't "programmable" in the same way as PLDs. More like a 2 input mux (I don't recall the exact details) intended so you can wire it into your c ircuit to be a number of different types of 2 or 3 input gates. The goal i s to replace multiple part numbers with a single line item in the BOM. Her e is one just emailed to me recently.

Rick C.