Quote:
Originally Posted by
cyberfish
Between 1.5V and 3.0V, it's undefined behaviour. It could be one or zero, or sometimes one and sometimes zero, depends on the phase of the moon. In reality, there is a voltage, somewhere between 1.5V and 3.0V, where the actual switching happens (Vth, the threshold voltage).
Not exactly. These days most digital inputs are schmidt triggers which do not have ambiguous intermidiate behaviors. What happens is that as voltage rises, it will switch 0 to 1 at 3.0v then as it falls it will switch from 1 to 0 at 1.5v... between those voltages it will retain it's previous state. The bad old days of using 7400 chips as "fuzz box" amplifiers are long gone.
Quote:
In your circuit, you are depending on this voltage, which is bad, because it's not a specified parameter, meaning, for example, for this batch of chips, it could be 2.0V, and for the next batch, it could be 2.5V. It's generally bad to rely on unspecified parameters. The behaviour of your circuit will change when Atmel changes their manufacturing process for example, even though their chips still meet the specs.
Hense the reason for schmidt triggers....