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For an all 5v system interfacing to CMOS components, do I select: TTL or LVCMOS/LVTTL? I'm guessing the latter as that would drive VOH up higher than 2.4v (TTL) but the 'low voltage' throws a wrench into that and is (perhaps?) not relevant?
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If its an all 5V system, then why would you suggest you are using VCCIO = 3.3V? :)
I'm not sure that anything really changes in the I/O cells based on these selections. I recall that selecting between standards gives you more current drive options in some of the newer devices, but I don't recall the FLEX10Ks as having a lot of flexibility. It may be that these settings are more "you telling the tool about the PCB" rather than the tool using those settings to set a bit in the configuration bit stream.
Either way, the I/Os are 5V tolerant, so you can try both. Generate a toggling signal and look at it with a scope for each setting.
Cheers,
Dave
Honored Contributor
