RTU: Add _onRequest on illegal function

Author: emelianov

src/Modbus.cpp

@@ -431,7 +431,10 @@ void Modbus::slavePDU(uint8_t* frame) {
         break;
 
         default:
-            exceptionResponse(fcode, EX_ILLEGAL_FUNCTION);
+            ex = _onRequest(fcode, {frame + 1});
+            if (ex != EX_PASSTHROUGH) {
+                exceptionResponse(fcode, EX_ILLEGAL_FUNCTION);
+            }
             return;
     }
 }

src/Modbus.h

@@ -153,6 +153,7 @@ class Modbus {
                 uint16_t andMask;
                 uint16_t orMask;
             };
+            uint8_t* data;
             RequestData(TAddress r1, uint16_t c1) {
                 reg = r1;
                 regCount = c1;
@@ -168,6 +169,9 @@ class Modbus {
                 andMask = m1;
                 orMask = m2;
             };
+            RequestData(uint8_t* d) {
+                data = d;
+            };
         };
 
 	    struct frame_arg_t {