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Digital Pin Trigger Levels
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Digital Pin Trigger Levels

by cciarleg on Wed Aug 10, 2011 7:18 pm


I can't seem to find this information anywhere.

Does anyone know at what voltage level the pins on the Atmega register a "high"? The setup is an Atmega328p running on a 5V supply.

Just to be clear, if I have an input discrete line being pulled high, what voltage does that need to be pulled to to get it to register on the Atmega? I know that 5 is ideal, but I am looking for the minimum level.

My problem is that I have a serial line with a "high" of 3.25 and I want to know if that is going to work if the Atmega is running at 5V. Its attached to a GPS that runs on 5V but only can output a max of 3.25 on its pins for the serial communications.

If not, I am relatively new to electronics, would I be looking for an op-amp or something to make that signal recognizable?

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Joined: Sun Jul 24, 2011 12:23 pm

Re: Digital Pin Trigger Levels

by scott_42 on Wed Aug 10, 2011 8:26 pm

From the data sheet which has lots of valuable info. You should pick up a copy.
VIH (Input High Voltage, except XTAL1 and RESET pins) @ Vcc 2.4…5.5V
Min: 0.6Vcc
Max: Vcc + 0.5

Given your 5V example, minimum is 5.0V * 0.6 = 3.0V. You are cutting is close with the 3.25V but it should work according to the spec.

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Please be positive and constructive with your questions and comments.