diff --git a/quantum/split_common/serial.h b/quantum/split_common/serial.h
index e566eb8a06..fb91ffdaeb 100644
--- a/quantum/split_common/serial.h
+++ b/quantum/split_common/serial.h
@@ -1,21 +1,20 @@
 #ifndef MY_SERIAL_H
 #define MY_SERIAL_H
 
-#include "config.h"
 #include <stdbool.h>
 
-/* TODO:  some defines for interrupt setup */
-#define SERIAL_PIN_DDR DDRD
-#define SERIAL_PIN_PORT PORTD
-#define SERIAL_PIN_INPUT PIND
-#define SERIAL_PIN_MASK _BV(PD0)
-#define SERIAL_PIN_INTERRUPT INT0_vect
-
-#define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
-#define SERIAL_MASTER_BUFFER_LENGTH 1
-
-// Address location defines 
-#define SERIAL_BACKLIT_START   0x00
+// ///////////////////////////////////////
+//  Need Soft Serial defines in config.h
+// ///////////////////////////////////////
+// eg.
+// #define SERIAL_PIN_DDR DDRD
+//  #define SERIAL_PIN_PORT PORTD
+//  #define SERIAL_PIN_INPUT PIND
+//  #define SERIAL_PIN_MASK _BV(PD0)
+//  #define SERIAL_PIN_INTERRUPT INT0_vect
+//
+// #define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
+// #define SERIAL_MASTER_BUFFER_LENGTH 1
 
 // Buffers for master - slave communication
 extern volatile uint8_t serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH];
diff --git a/quantum/split_common/serial_backward_compatibility.h b/quantum/split_common/serial_backward_compatibility.h
new file mode 100644
index 0000000000..e9f5890650
--- /dev/null
+++ b/quantum/split_common/serial_backward_compatibility.h
@@ -0,0 +1,15 @@
+/* serial.h backward compatibility */
+
+#ifndef SERIAL_PIN_DDR
+ #define SERIAL_PIN_DDR DDRD
+ #define SERIAL_PIN_PORT PORTD
+ #define SERIAL_PIN_INPUT PIND
+ #define SERIAL_PIN_MASK _BV(PD0)
+ #define SERIAL_PIN_INTERRUPT INT0_vect
+#endif
+
+#ifndef SERIAL_SLAVE_BUFFER_LENGTH
+ #define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
+ #define SERIAL_MASTER_BUFFER_LENGTH 1
+#endif
+
diff --git a/quantum/split_common/split_util.h b/quantum/split_common/split_util.h
index d6cf3e72a9..45e8db0f2f 100644
--- a/quantum/split_common/split_util.h
+++ b/quantum/split_common/split_util.h
@@ -7,6 +7,9 @@
 #include <stdlib.h>
 #include "eeconfig.h"
 
+// backlight level store index in serial_master_buffer[] for slave to read
+#define SERIAL_BACKLIT_START   0x00
+
 #define SLAVE_I2C_ADDRESS           0x32
 
 extern volatile bool isLeftHand;