unsigned long previousMillis = 0;
const long interval = 250;
int responseO;
int responseR;

void setup() {

Serial.begin(9600);
while (!Serial);

}

void loop() {

unsigned long currentMillis = millis();

if (currentMillis - previousMillis >= interval) //timer for every 250ms
{

previousMillis = currentMillis;

Serial.println("R");               //Figured that "println" with a string for the character R should be ok
if(Serial.available() >0)          //Don't know if I am correct here, I was hoping that the serial would only be read if the device responded to the command R
{responseR = Serial.read();}       //Read serial for device's response to command R and save it in a variable


Serial.println("O");               //Do the same thing for the command O
if(Serial.available() >0)
{responseO = Serial.read()}

}

}