Depends upon the parts family. CMOS want .7 * Vcc (3.5V), Schmidt inputs
often want to see .8 * Vcc (4V). TTL will let you get away with as little
as 2V. Your best bet is to consult the datasheet(s). This seems pretty
But generally you have an easy "hi" in the voltage supply to
If you need something set "hi" permanently, you tie it to the supply
With TTL, it's suggested that a current limiting resistor be used,
but a lot got away without them.
And if this is connected to some external point, you'd want to use
a resistor so when that point gets switched to ground it doesn't
short out the supply voltage.
But the resistors are there not to fiddle with voltage, but to
limit current at the input of the device.
You need to be specific if you have something else in mind. Because
if you aren't using the supply voltage as your "hi", then likely you
are talking about some external source, and in those cases you likely
don't want to just apply that voltage directly into logic IC inputs.