In the datasheet for most IC's it stands that:

Vil/Vih 0,8/2,0

So does it mean that when the pin is off/inactive (low) the voltage that comes out of it is 0,8 , and when it is on/active (high) the voltage is 2,0?

correct me if im wrong.

Cheers!
Lac.

 

Hi.
If I remember correctly it means less than 0.8 Volts is considered as low (0) and more than 2.0 Volts is high (1). The interval in-between is not allowed.

Ante :roll:

 

ok. But how do I know what voltage goes out from the pins? Is the same as the input voltage (+5VDC)?

Thanks!
Lac.

 

It's a logic chip, you don't need to know the voltage!, just that it will be below 0.8V for a low and above 2V for a high - anything you connect it to should comply with the same logic standard. For most practical purposes you can assume 0V and 5V, although it probably won't quite reach either extreme.

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It would be in a perfect world, but it is normally a little less than the supply.

Ante :roll:

 

ViL = Maximum input voltage that will be recognized as a logic LOW level
Vih = Minimum input voltage that will be recognized as a logic HIGH level

This is incidentally the TTL standard and Nigel is correct that for the most part you don't have to worry about these other than for two important exceptions:

1) When your circuit doesnt work! being the skilled troubleshooter you are, you'll want to know these levels as you poke around your circuit looking for the wiring goof-up or in some cases, the smoked part.

2) When you are interfacing two different logic families together. So, you want to connect your TTL and gate directly to a Pentium pro that uses GTL inputs, you will recognize that it won't work.

 

The guaranteed output voltage levels are Voh/Vol.