Is "Output, Driving Ground" same as out_pin <='0';

You're right. I haven't been back-annotating.

When I tried to back-annotate, it recommended writing vqm file instead.

I tried the vqm route and I tried the back-annotate route.

With my EP1C6 design it seems to generate different files a lot!

Even just back-annotating and then recompiling with no other changes, the rbf/ttf output files are different!

I think I will explicity drive these outputs to ground from within the VHDL.

I would prefer my unused pins default to input with weak pullup. (safer default!)

Hopefully the IO is just "as good a ground" with this approach.

I can't see any reason they wouldn't use the same transistor for both data and SSN grounding functions ... unless the SSN transistor is bigger/slower/lowerRDSon ... hmmm

Oh well.

If anyone knows ... I'm listening.

Thanks

Steve