Digital circuit inputs turn on thesholds, turn on voltage?

[danny davis]

The chip you're testing is already connected to ground and +5V (or whatever it's supply voltage is). That's all you need. For logic level low, connect the input to ground. For logic level high, connect the input to ground. +5V (or whatever the supply voltage is).

I will not be able to find out the inputs thresholds voltage level of the IC chips input If I supply it with +5 volts, I need to know when the IC chip switch states at what input threshold voltage level

Supply +5 volts on the input will not tell me at what input threshold voltage level the IC chip is

 

[Audioguru]

The threshold voltage of a logic IC does not matter because it is fixed during manufacturing and it does not change if the IC fails.
Simply learn what the low and high input and output voltages are for TTL and for Cmos.

 

[ebclr]

Cmos use very low power TTL use veru Hugh power
Cmos have a extremelly high fani in / fanout While TTL not
Cmos can be used in many VCC from 2 to 15 V TTL only 5V

Both are deprecated Technologies no more in use in new designer, Fpga do all things faster, cheaper and cooler

 

[BradtheRad]

I will not be able to find out the inputs thresholds voltage level of the IC chips input If I supply it with +5 volts, I need to know when the IC chip switch states at what input threshold voltage level

Supply +5 volts on the input will not tell me at what input threshold voltage level the IC chip is

A setup like this will reveal what happens when you gradually change the input volt level, and at the threshold which causes the output to change state:

A simulator will not necessarily act the way real components do.

The inverter has its threshold at the middle between supply V and 0 V (at least it is with the 4069UBE).
However not all logic chips behave exactly this same way. They respond according to the range of logic levels for a given family of IC's. Some have hysteresis action.

It is also instructive to leave an input disconnected, and see what output you get. I have seen a chip producing 60 Hz square waves, due to ambient AC mains hum getting into it even though there is no direct connection.