> If you need 5V compatibility...

The devil in the details is that when 5V-tolerant I/O are naively configured as such, device reliability drops like a rock. You'll likely find this disclosed in the manual fine print. Something to consider when prototyping a design destined for production.

In these boards it's not "5V tolerant". It's actual 5V I/O. EPF10K70. They are obsolete, and so the production part doesn't apply. Solely for hobby stuff.

Fair enough.

What's the software requirement side look like? Intel's website[1; under Legacy Devices] says Quartus II v9.0 was the latest release that could target FLEX 10K devices. Doesn't look like you can download that release anymore, and liable to run into compatibility issues just installing on modern OSs without a VM.

[1] https://fpgasoftware.intel.com/devices/

This only became an issue a few months ago, and it's really annoying if you need older software. Intel/Altera's site used to let you download older releases; it now redirects to a discontinuation notice.

> ...and it's really annoying if you need older software.

Bummer, and a real shame given how seemingly common regressions are in this space. Not my specialization, but anecdotally over a decade or so, I've encountered scenarios on MAX 7000 and Cyclone II (Quartus II v9.0 builds, v10.x breaks), Virtex-7 (Vivado v2018.3 builds, v2019.1 breaks) and Virtex-5 (ISE v14.6 builds, v14.7 breaks).

What do people need 5V for these days?

External stepper motor drivers. eg:

http://leadshine.com/ProductSubType.aspx?type=products&categ...

Driving a stepper directly from FPGA? Why?

Seemed to be more a question of "why 5v at all?", rather than meaning FPGA-specific. ;)

I have a lot of old 8 bit computers, and there's many interesting things you can do with a native 5v FPGA or CPLD there.

I assume interfacing simply with cheap ATMEL and PIC MCUs is another use case.

The university boards can also support 3.3v.

A lot of cheap Atmel micros can run at 3.3v and I think at least some go down to 2.7v.

I need 5v but I don't think any of the few FPGA chips that support 5v are actually usable with the Symbiflow stack.

I do wonder what's the best way to translate to 5v and back. There has to be some fast-switching, go-to part for the purpose.

Unfortunately, there's not a good single solution. Best depends on single vs bi-directional (also, which direction), switching speed, tristate or not, etc.

I do pretty much need to interface a 68000 bus.

D lines and some signals need to be bidirectional. And I might even need to do bus mastering, so most signals would have to be.

This doc might be useful:

http://marc.retronik.fr/motorola/68K/68000/The_68000_and_its...

And, yeah...you have some work ahead. Lots of bi-directional, tristate, open drain, totem pole/push-pull, etc.

Yes, a major pita. Mainly afraid of not groking the bus and driving the bus at the same time as the 68k. The working idea is to use a bunch of some sort of voltage translator chip (finding the right one for this is the pain point), and imposing constraints so that if the CPU is driving the address or data bus as signaled by e.g. /AS or the R/W signal, then the translators won't drive it. With a bunch of 74s or a CPLD in the 5v side.

I didn't have that one PDF, so I saved it for safe-keeping with my other 68k stuff. Thanks.