diffferences between a TTL and a ST (Schmitt Trigger) I/O ??

[foosm]

hi there, may i ask what is the difference between a TTL and a ST (Schmitt Trigger) I/O ???

i know the definition of a TTL is that the high state = ON = +5V and the low state = OFF = 0V. But how about Schmitt Trigger ???

thanks a lot

 

[ivancho]

TTL......Transistor to Transistor logic... here as you said the voltae level for the logic is 5V for a 1 (high) or 0V for a zero (Low). Actually those voltages range have some tolerance, as you can see in the attached image (taken from I hoe they don't mind :cry: ) .

Schmitt Trigger inputs are different, they are set up so that they work around their hysteresis. **broken link removed** you can find areally good explanation on how it works. In a simple phrase: The output on a Schmitt Trigger will only be high after passing a set reference votage A, and will turn low at a lower reference voltage B.

Schmitt Trigger is good when you have a noisy input and you want a clean digital output which could be TTL.

Hope it helps

Ivancho

 

[TheAnimus]

one thing to be careful about is what type of each level ur looking at in your project, 3.3v,3.0v,5v,15v,9.somthing-very-strange v
are all such types i have used recently
5v been the most common.

A quick check of the datasheet's electrical characteristics is always good, some devices are often 0.2v outside of the TTL standard they claim to work on!