FPGA Central

Hi Luiz,
I'll try to comment.

> The manual says:
> Vout = low, if Vin <= Vref - 0.5
> Vout = high, if Vin >= Vref + 0.5
> But, what does hapen if Vin=Vref+0.1?
I see other numbers in document "Spartan-IIC and Switching
Characteristics" (table on pg.3).
Inequations should be as following:
Vout = low, if Vin <= Vref - 0.1
Vout = high, if Vin >= Vref + 0.1(volts, here and below)

> Does Vout still go high?
Suppose Vin=Vref+0.02 in your question to match corrected inequations.
Vout will not go high. As you are breaking the logical input level
requirements hence the input buffer will behave like non-linear
differential amplifier (so it is always possible to find such Vin
value on DC input-to-output transfer curve that Vout will stand
between Vhigh and Vlow,
say Vout=(Vhigh+Vlow)/2+Voffset and this point will be stable if Vin
is stable).

> I think this is related to the metastability problem, but I preferred
> to start a new thread.
I don't think this is about metastability unless you bring positive
feedback to input buffer.

This is only my opinion, I can't verify it with measurements,
unfortunately.

Regards,
Andrey