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

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New Member
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


New Member
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 this site I hoe they don't mind :cry: ) .

Schmitt Trigger inputs are different, they are set up so that they work around their hysteresis. Here 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




New Member
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!
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