I am using PIC18F and currently trying to interface it with SIM900. I am using UART Rx interrupt. ISR is working correctly but I wonder how to get data in main loop. Lets say :

#pragma interrupt hi_prioriint
void hi_prioriint(void)
{
   if(PIR1bits.RCIF==1)
   {
      Rx = ReadUSART();  //store the received byte in Rx
   }
 }

Now I want to use Rx in main loop. For example, if I send AT command then I need to check if I received OK or ERROR from SIM900. (For the time being I am just testing it with a single byte and will convert it later into receiving strings because response from the SIM900 is in string form)

Example:

 putrsUSART("AT\r");        //sending AT command
 delay(500)                 //delay of 500ms
 if(strcmp(Rx,"OK")==0)     //checking the response
 {
    //if received OK then proceed further
 }

So how to use RX data of ISR in main loop.? Please guide.