diff --git a/grbl/cpu_map.h b/grbl/cpu_map.h
index 0e2b25e5..49d9a252 100644
--- a/grbl/cpu_map.h
+++ b/grbl/cpu_map.h
@@ -26,27 +26,42 @@
 #ifndef cpu_map_h
 #define cpu_map_h
 
-
 #ifdef CPU_MAP_ATMEGA328P // (Arduino Uno) Officially supported by Grbl.
 
-  // Define serial port pins and interrupt vectors.
+// Uncomment to use a CNC SHIELD v4, the one for arduino nano
+// #define CNC_SHIELD_V4
+
+// Define serial port pins and interrupt vectors.
   #define SERIAL_RX     USART_RX_vect
   #define SERIAL_UDRE   USART_UDRE_vect
 
   // Define step pulse output pins. NOTE: All step bit pins must be on the same port.
   #define STEP_DDR        DDRD
   #define STEP_PORT       PORTD
-  #define X_STEP_BIT      2  // Uno Digital Pin 2
-  #define Y_STEP_BIT      3  // Uno Digital Pin 3
-  #define Z_STEP_BIT      4  // Uno Digital Pin 4
+  #ifndef CNC_SHIELD_V4  // has traces for step and direction interchanged
+    #define X_STEP_BIT      2  // Uno Digital Pin 2
+    #define Y_STEP_BIT      3  // Uno Digital Pin 3
+    #define Z_STEP_BIT      4  // Uno Digital Pin 4
+  #else
+    #define X_STEP_BIT      5  // nano Digital Pin 5
+    #define Y_STEP_BIT      6  // nano Digital Pin 6
+    #define Z_STEP_BIT      7  // nano Digital Pin 7
+  #endif
   #define STEP_MASK       ((1<<X_STEP_BIT)|(1<<Y_STEP_BIT)|(1<<Z_STEP_BIT)) // All step bits
 
   // Define step direction output pins. NOTE: All direction pins must be on the same port.
   #define DIRECTION_DDR     DDRD
   #define DIRECTION_PORT    PORTD
-  #define X_DIRECTION_BIT   5  // Uno Digital Pin 5
-  #define Y_DIRECTION_BIT   6  // Uno Digital Pin 6
-  #define Z_DIRECTION_BIT   7  // Uno Digital Pin 7
+
+  #ifndef CNC_SHIELD_V4  // has traces for step and direction interchanged
+    #define X_DIRECTION_BIT   5  // Uno Digital Pin 5
+    #define Y_DIRECTION_BIT   6  // Uno Digital Pin 6
+    #define Z_DIRECTION_BIT   7  // Uno Digital Pin 7
+  #else
+    #define X_DIRECTION_BIT   2  // nano Digital Pin 2
+    #define Y_DIRECTION_BIT   3  // nano Digital Pin 3
+    #define Z_DIRECTION_BIT   4  // nano Digital Pin 4
+  #endif
   #define DIRECTION_MASK    ((1<<X_DIRECTION_BIT)|(1<<Y_DIRECTION_BIT)|(1<<Z_DIRECTION_BIT)) // All direction bits
 
   // Define stepper driver enable/disable output pin.