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 Inputs provides us PNP input.

Inputs:  (10x) Digital Isolated (5-24Vdc), (5x) can work like interrupt INT (7-24Vdc).

Know more about Digital Inputs.

Know more about PNP Inputs.

TYPICAL CONNECTION

- Digital Isolated Input

- Digital No Isolated Input 

INTERRUPT INPUTS

Interrupt Service Rutine.  A mechanism that allows a function to be associated with the occurance 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. 

Inputs:   (5x) Interrupt Inputs (7-24Vdc). “Can work like Digital Input (24Vdc)”.

Interrupt	Arduino Mega Pin	M-Duino Pin
INT1	3	I0.6/INT1
INT2	19	I1.6/INT2
INT3	18	I1.5/INT3
INT4	21	I2.1/INT4
INT5	20	I2.0/INT5

    - I0.6 also as Pin3 enables Interrupts turning ON the switch number 4 of down communication switch.
    - I1.5 and I1.6 also as Tx1 and Rx1. Enable Interrupts turning ON the switches number 1 and 2 of up communication switches.
    - I2.0 and I2.1 also as SCA and SCL. Enable Interrupts turning ON the switches number 3 and 4 of up communication switches. In this case you won’t be able to use I2C.

TYPICAL CONNECTION

In this example we activate INT1 using pin I0_6 from M-duino board. When there’s a change   

#define INTERRUPT I0_6 //other pins: 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;
}