Voltage variation between –Vcc (or GND) and +Vcc, can take any value. An analog input provides a coded measurement in the form of a digital value with an N-bit number.
In Digital and Analog I/O there’s self insulation, so its posible to connect them in a different power supply than 24 V.  

To know more about analog inputs... 

Voltage variation from –Vcc (or GND) to +Vcc, with no intermediate values. Two states: 0 (-Vcc or GND) and 1 (+Vcc).
In Digital and Analog I/O there’s self insulation, so its posible to connect them in a different power supply than 24 V.  

Digital PNP Inputs
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What is an Interrupt Service Routine?
A mechanism that allows a function to be associated with the occurrence of a particular event. When the event occurs the processor exits immediately from the normal flow of the program and runs the associated ISR function ignoring any other task. 

If you want to know more about interrupt inputs...

#define INTERRUPT I0_5 //other pins: I0_6, I2_6, I2_5, I1_6, I1_5 (M-Duino) I0_0, I0_3, I0_2, I0_1 (Ardbox)

volatile bool state = false;

void setup() {
  pinMode(INTERRUPT, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(INTERRUPT), function_call_back, CHANGE);
}

void loop() {
  if (state == true){
    Serial.println("Interrupt activated");
    state = false;
  }
}

void function_call_back(){ //Change led state
  state = true;
}

If you want to know everything about inputs, outputs and the detail of Analog, Digital, Interrupt or PWM, you can download this Guide.

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