For 5v “HIGH” is 5v and “LOW” is 0v, right?

Well, not quite - having inadvetently created a voltage divider on an input to an IC I found it isn’t quite the case!

So a bit of research starting with the datasheet for the IC revealed nowt.

More general research (my friend google) came up with the following definitions for a 5v supply

LOW = 0 - 1.5 v

HIGH = 3.5 - 5v

But I couldn’t find a formula for calculating different values for different voltages, or even whether this is an industry standard for IC’s.

Does anyone know of such a formula,or can provide a link to one?

Thanks - Richard