-#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
+//////////////// for backward compatibility ////////////////////////////////
+#if !defined(SERIAL_USE_SINGLE_TRANSACTION) && !defined(SERIAL_USE_MULTI_TRANSACTION)
+/* --- USE 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