Catch Low level on INT0

Sorry for noob question
I have some external line (pin) where usually high level (2.8V) on it and some times low level (20ms)
how connect -
is it enough connect this external pin direct to D2 (Nano board) without resistor (pullup/pulldown/etc) ? pls find attach

and how setup pin and interrupt to catch low level

pinMode(2, INPUT); 
pinMode(2, INPUT_PULLUP);
attachInterrupt(0, blink, CHANGE);
attachInterrupt(0, blink, LOW;
attachInterrupt(0, blink, FALLING );

Never use LOW - the interrupt will trigger as long as the condition persists.

I'd use FALLING.

Please describe the device that is providing the "external signal".

It is not safe to connect powered external equipment to an input on an unpowered Arduino, without using a series resistor (typically 10K).

A or B ? and HIGH as I mentioned is 2.8V
device is gsm modem

ok, but how setup

pinMode(2, INPUT); 
pinMode(2, INPUT_PULLUP);

A) to protect the input.

For a 5V Nano, 2.8V is not a HIGH. A high (Vih) for a 5V ATmega328 chip is 0.6 * Vcc = 0.6 * 5V = 3.0V. See page 258 of the data sheet.

Option A is "a series resistor" but it should be 10K. And do take note of @groundFungus comment.

You need a level shifter for a 2.8V signal, or use a 3.3V Arduino.

But the option is there (Fig-1):


So use it.

(Did you imagine I didn't know it was an option?)

You might have a good reason to discourage the use of this (AL) option.

What's that?

Some esoteric jargon?

Left-top of Fig-1 of Post-8.

Yes, but what is it?
I can't find that figure in the processor datasheet - where did it come from?
What does "AL" mean, in terms a person familiar with the processor family would understand?

(Esoteric jargon?)

At the left-top of Fig-1 of Post-8, there are other acronymes like FE, RE, and AH; but, why have you been particulalry interested for AL? It is for Awami League - the Ruling Party of Bangladesh. Do you believe?

Do you understand "esoteric"?

Because it was the one you quoted.

Welcome to my mute list.

I have tried on 5v micro board (I think on Nano will be the same)

with direct connect w/o resistor and I catch it (low level) successfully

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