diff --git a/keyboards/helix/rev1/keymaps/OLED_sample/serial_config.h b/keyboards/helix/rev1/keymaps/OLED_sample/serial_config.h
index 289a165fa3..b991b874b7 100644
--- a/keyboards/helix/rev1/keymaps/OLED_sample/serial_config.h
+++ b/keyboards/helix/rev1/keymaps/OLED_sample/serial_config.h
@@ -8,6 +8,9 @@
 #define SERIAL_PIN_MASK _BV(PD2)
 #define SERIAL_PIN_INTERRUPT INT2_vect
 
+#define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
+#define SERIAL_MASTER_BUFFER_LENGTH 0
+
 //// #error rev1/keymaps/OLED_sample serial config
 
 #endif /* SOFT_SERIAL_CONFIG_H */
diff --git a/keyboards/helix/rev1/matrix.c b/keyboards/helix/rev1/matrix.c
index 6613c02b00..f2506868ea 100644
--- a/keyboards/helix/rev1/matrix.c
+++ b/keyboards/helix/rev1/matrix.c
@@ -35,7 +35,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifdef USE_MATRIX_I2C
 #  include "i2c.h"
 #else // USE_SERIAL
-#  include "split_scomm.h"
+#  include "serial.h"
 #endif
 
 #ifndef DEBOUNCE
@@ -178,7 +178,7 @@ i2c_error: // the cable is disconnceted, or something else went wrong
 int serial_transaction(void) {
     int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
 
-    if (serial_update_buffers(1)) {
+    if (serial_update_buffers()) {
         return 1;
     }
 
diff --git a/keyboards/helix/rev1/rules.mk b/keyboards/helix/rev1/rules.mk
index 5ecfa33a2a..13834f5da1 100644
--- a/keyboards/helix/rev1/rules.mk
+++ b/keyboards/helix/rev1/rules.mk
@@ -1,5 +1,4 @@
 SRC += rev1/matrix.c
 SRC += rev1/split_util.c
-SRC += rev1/split_scomm.c
 
 BACKLIGHT_ENABLE = no
diff --git a/keyboards/helix/rev1/serial_config.h b/keyboards/helix/rev1/serial_config.h
index f021d6e04b..51c6aa3750 100644
--- a/keyboards/helix/rev1/serial_config.h
+++ b/keyboards/helix/rev1/serial_config.h
@@ -8,6 +8,9 @@
 #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 0
+
 /// #error rev1 serial config
 
 #endif /* SOFT_SERIAL_CONFIG_H */
diff --git a/keyboards/helix/rev1/split_scomm.c b/keyboards/helix/rev1/split_scomm.c
deleted file mode 100644
index a5c0485e30..0000000000
--- a/keyboards/helix/rev1/split_scomm.c
+++ /dev/null
@@ -1,36 +0,0 @@
-#ifdef USE_SERIAL
-#include <stdbool.h>
-#include <stdint.h>
-#include <stddef.h>
-#include <split_scomm.h>
-#include "serial.h"
-
-uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
-uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
-uint8_t volatile status0 = 0;
-
-SSTD_t transactions[] = {
-    { (uint8_t *)&status0,
-      sizeof(serial_master_buffer), (uint8_t *)serial_master_buffer,
-      sizeof(serial_slave_buffer), (uint8_t *)serial_slave_buffer
-    }
-};
-
-void serial_master_init(void)
-{
-    soft_serial_initiator_init(transactions);
-}
-
-void serial_slave_init(void)
-{
-    soft_serial_target_init(transactions);
-}
-
-// 0 => no error
-// 1 => slave did not respond
-// 2 => checksum error
-int serial_update_buffers(int master_update)
-{
-    return soft_serial_transaction();
-}
-#endif /* USE_SERIAL */
diff --git a/keyboards/helix/rev1/split_scomm.h b/keyboards/helix/rev1/split_scomm.h
deleted file mode 100644
index c81eff4ffe..0000000000
--- a/keyboards/helix/rev1/split_scomm.h
+++ /dev/null
@@ -1,15 +0,0 @@
-#ifndef SPLIT_COMM_H
-#define SPLIT_COMM_H
-
-// Buffers for master - slave communication
-#define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
-#define SERIAL_MASTER_BUFFER_LENGTH 1
-
-extern volatile uint8_t serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH];
-extern volatile uint8_t serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH];
-
-void serial_master_init(void);
-void serial_slave_init(void);
-int serial_update_buffers(int master_changed);
-
-#endif /* SPLIT_COMM_H */
diff --git a/keyboards/helix/rev1/split_util.c b/keyboards/helix/rev1/split_util.c
index fe17e14f84..5debd6e00b 100644
--- a/keyboards/helix/rev1/split_util.c
+++ b/keyboards/helix/rev1/split_util.c
@@ -12,7 +12,7 @@
 #ifdef USE_MATRIX_I2C
 #  include "i2c.h"
 #else
-#  include "split_scomm.h"
+#  include "serial.h"
 #endif
 
 volatile bool isLeftHand = true;
diff --git a/keyboards/helix/rev2/keymaps/default/config.h b/keyboards/helix/rev2/keymaps/default/config.h
index cf9c8e5e39..185e678385 100644
--- a/keyboards/helix/rev2/keymaps/default/config.h
+++ b/keyboards/helix/rev2/keymaps/default/config.h
@@ -22,7 +22,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define CONFIG_USER_H
 
 // if you need more program area, try uncomment follow line
-//#undef SERIAL_USE_MULTI_TRANSACTION
+//#include "serial_config_simpleapi.h"
 
 // place overrides here
 
diff --git a/keyboards/helix/rev2/keymaps/edvorakjp/config.h b/keyboards/helix/rev2/keymaps/edvorakjp/config.h
index 51cd1d6417..ead31605b2 100644
--- a/keyboards/helix/rev2/keymaps/edvorakjp/config.h
+++ b/keyboards/helix/rev2/keymaps/edvorakjp/config.h
@@ -2,7 +2,7 @@
 #define CONFIG_USER_H
 
 // if you need more program area, try uncomment follow line
-//#undef SERIAL_USE_MULTI_TRANSACTION
+//#include "serial_config_simpleapi.h"
 
 #undef TAPPING_FORCE_HOLD
 #undef TAPPING_TERM
diff --git a/keyboards/helix/rev2/keymaps/five_rows/config.h b/keyboards/helix/rev2/keymaps/five_rows/config.h
index 7e7daf0f64..8372194604 100644
--- a/keyboards/helix/rev2/keymaps/five_rows/config.h
+++ b/keyboards/helix/rev2/keymaps/five_rows/config.h
@@ -22,7 +22,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define CONFIG_USER_H
 
 // if you need more program area, try uncomment follow line
-//#undef SERIAL_USE_MULTI_TRANSACTION
+//#include "serial_config_simpleapi.h"
 
 #undef TAPPING_TERM
 #define TAPPING_TERM 140
diff --git a/keyboards/helix/rev2/keymaps/five_rows_jis/config.h b/keyboards/helix/rev2/keymaps/five_rows_jis/config.h
index 8cdfdb4e72..c380b7db4e 100644
--- a/keyboards/helix/rev2/keymaps/five_rows_jis/config.h
+++ b/keyboards/helix/rev2/keymaps/five_rows_jis/config.h
@@ -24,7 +24,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 // place overrides here
 
 // if you need more program area, try uncomment follow line
-//#undef SERIAL_USE_MULTI_TRANSACTION
+//#include "serial_config_simpleapi.h"
 
 #ifdef MOUSEKEY_ENABLE
   #undef MOUSEKEY_INTERVAL
diff --git a/keyboards/helix/rev2/keymaps/froggy/config.h b/keyboards/helix/rev2/keymaps/froggy/config.h
index a1fea15067..dad2483034 100644
--- a/keyboards/helix/rev2/keymaps/froggy/config.h
+++ b/keyboards/helix/rev2/keymaps/froggy/config.h
@@ -22,7 +22,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define CONFIG_USER_H
 
 // if you need more program area, try uncomment follow line
-//#undef SERIAL_USE_MULTI_TRANSACTION
+//#include "serial_config_simpleapi.h"
 
 #undef TAPPING_TERM
 #define TAPPING_TERM 200
diff --git a/keyboards/helix/rev2/keymaps/led_test/config.h b/keyboards/helix/rev2/keymaps/led_test/config.h
index 56d5f91345..0438254528 100644
--- a/keyboards/helix/rev2/keymaps/led_test/config.h
+++ b/keyboards/helix/rev2/keymaps/led_test/config.h
@@ -22,7 +22,7 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define CONFIG_USER_H
 
 // if you need more program area, try uncomment follow line
-#undef SERIAL_USE_MULTI_TRANSACTION
+#include "serial_config_simpleapi.h"
 
 // place overrides here
 
diff --git a/keyboards/helix/rev2/matrix.c b/keyboards/helix/rev2/matrix.c
index fd64c37ab1..322959dbbb 100644
--- a/keyboards/helix/rev2/matrix.c
+++ b/keyboards/helix/rev2/matrix.c
@@ -183,7 +183,11 @@ i2c_error: // the cable is disconnceted, or something else went wrong
 
 int serial_transaction(int master_changed) {
     int slaveOffset = (isLeftHand) ? (ROWS_PER_HAND) : 0;
+#ifdef SERIAL_USE_MULTI_TRANSACTION
     int ret=serial_update_buffers(master_changed);
+#else
+    int ret=serial_update_buffers();
+#endif
     if (ret ) {
         if(ret==2) RXLED1;
         return 1;
diff --git a/keyboards/helix/rev2/serial_config_simpleapi.h b/keyboards/helix/rev2/serial_config_simpleapi.h
new file mode 100644
index 0000000000..e2d22a41e7
--- /dev/null
+++ b/keyboards/helix/rev2/serial_config_simpleapi.h
@@ -0,0 +1,8 @@
+#ifndef SERIAL_CONFIG_SIMPLEAPI_H
+#define SERIAL_CONFIG_SIMPLEAPI_H
+
+#undef SERIAL_USE_MULTI_TRANSACTION
+#define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
+#define SERIAL_MASTER_BUFFER_LENGTH MATRIX_ROWS/2
+
+#endif // SERIAL_CONFIG_SIMPLEAPI_H
diff --git a/keyboards/helix/rev2/split_scomm.c b/keyboards/helix/rev2/split_scomm.c
index f37b783d8a..9719eb22ea 100644
--- a/keyboards/helix/rev2/split_scomm.c
+++ b/keyboards/helix/rev2/split_scomm.c
@@ -1,4 +1,7 @@
 #ifdef USE_SERIAL
+#ifdef SERIAL_USE_MULTI_TRANSACTION
+/* --- USE flexible API (using multi-type transaction function) --- */
+
 #include <stdbool.h>
 #include <stdint.h>
 #include <stddef.h>
@@ -12,19 +15,8 @@ uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
 uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
 uint8_t volatile status_com = 0;
 uint8_t volatile status1 = 0;
-#ifdef SERIAL_USE_MULTI_TRANSACTION
 uint8_t slave_buffer_change_count = 0;
 uint8_t s_change_old = 0xff;
-#endif
-
-#ifndef SERIAL_USE_MULTI_TRANSACTION
-SSTD_t transactions[] = {
-    { (uint8_t *)&status_com,
-      sizeof(serial_master_buffer), (uint8_t *)serial_master_buffer,
-      sizeof(serial_slave_buffer), (uint8_t *)serial_slave_buffer
-    }
-};
-#else
 
 SSTD_t transactions[] = {
 #define GET_SLAVE_STATUS 0
@@ -46,7 +38,6 @@ SSTD_t transactions[] = {
       sizeof(serial_slave_buffer), (uint8_t *)serial_slave_buffer
     }
 };
-#endif
 
 void serial_master_init(void)
 {
@@ -63,7 +54,6 @@ void serial_slave_init(void)
 // 2 => checksum error
 int serial_update_buffers(int master_update)
 {
-#ifdef SERIAL_USE_MULTI_TRANSACTION
     int status;
     static int need_retry = 0;
     if( s_change_old != slave_buffer_change_count ) {
@@ -77,10 +67,7 @@ int serial_update_buffers(int master_update)
 	status = soft_serial_transaction(PUT_MASTER_GET_SLAVE_STATUS);
     need_retry = ( status == TRANSACTION_END ) ? 0 : 1;
     return status;
-#else
-    int status;
-    status = soft_serial_transaction();
-    return status;
-#endif
 }
+
+#endif // SERIAL_USE_MULTI_TRANSACTION
 #endif /* USE_SERIAL */
diff --git a/keyboards/helix/rev2/split_scomm.h b/keyboards/helix/rev2/split_scomm.h
index daa680f8d2..873d8939d8 100644
--- a/keyboards/helix/rev2/split_scomm.h
+++ b/keyboards/helix/rev2/split_scomm.h
@@ -1,18 +1,24 @@
 #ifndef SPLIT_COMM_H
 #define SPLIT_COMM_H
 
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+/* --- USE Simple API (OLD API, compatible with let's split serial.c) --- */
+#include "serial.h"
+
+#else
+/* --- USE flexible API (using multi-type transaction function) --- */
 // Buffers for master - slave communication
 #define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
 #define SERIAL_MASTER_BUFFER_LENGTH MATRIX_ROWS/2
 
 extern volatile uint8_t serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH];
 extern volatile uint8_t serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH];
-#ifdef SERIAL_USE_MULTI_TRANSACTION
 extern uint8_t slave_buffer_change_count;
-#endif
 
 void serial_master_init(void);
 void serial_slave_init(void);
 int serial_update_buffers(int master_changed);
 
+#endif
+
 #endif /* SPLIT_COMM_H */
diff --git a/keyboards/helix/serial.c b/keyboards/helix/serial.c
index b030451248..11ceff0b37 100644
--- a/keyboards/helix/serial.c
+++ b/keyboards/helix/serial.c
@@ -16,6 +16,45 @@
 
 #ifdef USE_SERIAL
 
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+/* --- USE Simple API (OLD API, compatible with let's split serial.c) */
+  #if SERIAL_SLAVE_BUFFER_LENGTH > 0
+  uint8_t volatile serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH] = {0};
+  #endif
+  #if SERIAL_MASTER_BUFFER_LENGTH > 0
+  uint8_t volatile serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH] = {0};
+  #endif
+  uint8_t volatile status0 = 0;
+
+SSTD_t transactions[] = {
+    { (uint8_t *)&status0,
+  #if SERIAL_MASTER_BUFFER_LENGTH > 0
+      sizeof(serial_master_buffer), (uint8_t *)serial_master_buffer,
+  #else
+      0, (uint8_t *)NULL,
+  #endif
+  #if SERIAL_SLAVE_BUFFER_LENGTH > 0
+      sizeof(serial_slave_buffer), (uint8_t *)serial_slave_buffer
+  #else
+      0, (uint8_t *)NULL,
+  #endif
+  }
+};
+
+void serial_master_init(void)
+{ soft_serial_initiator_init(transactions); }
+
+void serial_slave_init(void)
+{ soft_serial_target_init(transactions); }
+
+// 0 => no error
+// 1 => slave did not respond
+// 2 => checksum error
+int serial_update_buffers()
+{ return soft_serial_transaction(); }
+
+#endif // Simple API (OLD API, compatible with let's split serial.c)
+
 #define ALWAYS_INLINE __attribute__((always_inline))
 #define NO_INLINE __attribute__((noinline))
 #define _delay_sub_us(x)    __builtin_avr_delay_cycles(x)
diff --git a/keyboards/helix/serial.h b/keyboards/helix/serial.h
index d3cf1743a3..d2b7fd8e60 100644
--- a/keyboards/helix/serial.h
+++ b/keyboards/helix/serial.h
@@ -3,9 +3,9 @@
 
 #include <stdbool.h>
 
-// ////////////////////////////////////////////
+// /////////////////////////////////////////////////////////////////
 // Need Soft Serial defines in serial_config.h
-// ////////////////////////////////////////////
+// /////////////////////////////////////////////////////////////////
 // ex.
 //  #define SERIAL_PIN_DDR DDRD
 //  #define SERIAL_PIN_PORT PORTD
@@ -13,8 +13,31 @@
 //  #define SERIAL_PIN_MASK _BV(PD?)   ?=0,2
 //  #define SERIAL_PIN_INTERRUPT INT?_vect  ?=0,2
 //
-//  When using multi-type transaction function, define the following macro.
-//   #define SERIAL_USE_MULTI_TRANSACTION
+// //// USE Simple API (OLD API, compatible with let's split serial.c)
+// ex.
+//  #define SERIAL_SLAVE_BUFFER_LENGTH MATRIX_ROWS/2
+//  #define SERIAL_MASTER_BUFFER_LENGTH 1
+//
+// //// USE flexible API (using multi-type transaction function)
+//  #define SERIAL_USE_MULTI_TRANSACTION
+//
+// /////////////////////////////////////////////////////////////////
+
+
+#ifndef SERIAL_USE_MULTI_TRANSACTION
+/* --- USE Simple API (OLD API, compatible with let's split serial.c) */
+#if SERIAL_SLAVE_BUFFER_LENGTH > 0
+extern volatile uint8_t serial_slave_buffer[SERIAL_SLAVE_BUFFER_LENGTH];
+#endif
+#if SERIAL_MASTER_BUFFER_LENGTH > 0
+extern volatile uint8_t serial_master_buffer[SERIAL_MASTER_BUFFER_LENGTH];
+#endif
+
+void serial_master_init(void);
+void serial_slave_init(void);
+int serial_update_buffers(void);
+
+#endif // USE Simple API
 
 // Soft Serial Transaction Descriptor
 typedef struct _SSTD_t  {