corrected Fwd/Rev LED logic in NmraDccMultiFunctionMotorDecoder example

added conditional compilation to use the newer Dcc.pin() method that used digitalPinToInterrupt() to determine the Ext Interrupt Number based on Arduino Pin to reduce confusion

examples/NmraDcc_ARD_DCCSHIELD/NmraDcc_ARD_DCCSHIELD.ino

@@ -26,6 +26,9 @@
 // Un-Comment the line below to Enable DCC ACK for Service Mode Programming Read CV Capablilty 
 #define ENABLE_DCC_ACK  15  // This is A1 on the Iowa Scaled Engineering ARD-DCCSHIELD DCC Shield
 
+// Define the Arduino input Pin number for the DCC Signal 
+#define DCC_PIN     2
+
 NmraDcc  Dcc ;
 
 struct CVPair
@@ -101,8 +104,14 @@ void setup()
   
   Serial.println("NMRA DCC Iowa Scaled Engineering ARD-DCCSHIELD Example");
   
-  // Setup which External Interrupt, the Pin it's associated with that we're using and enable the Pull-Up 
-  Dcc.pin(0, 2, 1);
+  // Setup which External Interrupt, the Pin it's associated with that we're using and enable the Pull-Up
+  // Many Arduino Cores now support the digitalPinToInterrupt() function that makes it easier to figure out the
+  // Interrupt Number for the Arduino Pin number, which reduces confusion. 
+#ifdef digitalPinToInterrupt
+  Dcc.pin(DCC_PIN, 0);
+#else
+  Dcc.pin(0, DCC_PIN, 1);
+#endif
   
   // Call the main DCC Init function to enable the DCC Receiver
   Dcc.init( MAN_ID_DIY, 10, CV29_ACCESSORY_DECODER, 0 );