TTL or ST? What is it?

[dhouston]

Some are using TTL and some are using ST.
What is the difference?

See the DC Characteristics section of the datasheet. TTL is Transistor-Transistor Logic. It takes lower voltage to trigger the input. ST is Schmitt Trigger which requires higher voltage to trigger the input.

[xnihilo]

I read some stoff on wikipedia.
I'm wondering why they didn't use either TTL or ST for all pins...
Moreover, do I need something special if it is TTL? Just a voltage of 5V, right?

[skimask]

I read some stoff on wikipedia.
I'm wondering why they didn't use either TTL or ST for all pins...
Moreover, do I need something special if it is TTL? Just a voltage of 5V, right?

Read some more stuff on wikipedia on "hysteresis".
Then some of the benefits and/or drawbacks of an ST input will become more clear...