diff --git a/Core/gb.c b/Core/gb.c
index 2d5fff4..0049590 100755
--- a/Core/gb.c
+++ b/Core/gb.c
@@ -503,6 +503,35 @@ void GB_set_rumble_callback(GB_gameboy_t *gb, GB_rumble_callback_t callback)
     gb->rumble_callback = callback;
 }
 
+void GB_set_serial_transfer_start_callback(GB_gameboy_t *gb, GB_serial_transfer_start_callback_t callback)
+{
+    gb->serial_transfer_start_callback = callback;
+}
+
+void GB_set_serial_transfer_end_callback(GB_gameboy_t *gb, GB_serial_transfer_end_callback_t callback)
+{
+    gb->serial_transfer_end_callback = callback;
+}
+
+uint8_t GB_serial_get_data(GB_gameboy_t *gb)
+{
+    if (gb->io_registers[GB_IO_SC] & 1) {
+        /* Internal Clock */
+        GB_log(gb, "Serial read request while using internal clock. \n");
+        return 0xFF;
+    }
+    return gb->io_registers[GB_IO_SB];
+}
+void GB_serial_set_data(GB_gameboy_t *gb, uint8_t data)
+{
+    if (gb->io_registers[GB_IO_SC] & 1) {
+        /* Internal Clock */
+        GB_log(gb, "Serial write request while using internal clock. \n");
+        return;
+    }
+    gb->io_registers[GB_IO_SB] = data;
+}
+
 void GB_set_sample_rate(GB_gameboy_t *gb, unsigned int sample_rate)
 {
     if (gb->audio_buffer) {
diff --git a/Core/gb.h b/Core/gb.h
index 9b1a64a..63ea824 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -162,6 +162,9 @@ typedef void (*GB_infrared_callback_t)(GB_gameboy_t *gb, bool on, long cycles_si
 typedef uint8_t (*GB_camera_get_pixel_callback_t)(GB_gameboy_t *gb, uint8_t x, uint8_t y);
 typedef void (*GB_camera_update_request_callback_t)(GB_gameboy_t *gb);
 typedef void (*GB_rumble_callback_t)(GB_gameboy_t *gb, bool rumble_on);
+typedef void (*GB_serial_transfer_start_callback_t)(GB_gameboy_t *gb, uint8_t byte_to_send);
+typedef uint8_t (*GB_serial_transfer_end_callback_t)(GB_gameboy_t *gb);
+
 
 typedef struct {
     enum {
@@ -418,7 +421,8 @@ typedef struct GB_gameboy_s {
     GB_camera_get_pixel_callback_t camera_get_pixel_callback;
     GB_camera_update_request_callback_t camera_update_request_callback;
     GB_rumble_callback_t rumble_callback;
-
+    GB_serial_transfer_start_callback_t serial_transfer_start_callback;
+    GB_serial_transfer_end_callback_t serial_transfer_end_callback;
     /* IR */
     long cycles_since_ir_change;
     long cycles_since_input_ir_change;
@@ -497,4 +501,13 @@ void GB_set_infrared_callback(GB_gameboy_t *gb, GB_infrared_callback_t callback)
 void GB_set_infrared_input(GB_gameboy_t *gb, bool state);
 void GB_queue_infrared_input(GB_gameboy_t *gb, bool state, long cycles_after_previous_change);
 void GB_set_rumble_callback(GB_gameboy_t *gb, GB_rumble_callback_t callback);
+
+/* These APIs are used when using internal clock */
+void GB_set_serial_transfer_start_callback(GB_gameboy_t *gb, GB_serial_transfer_start_callback_t callback);
+void GB_set_serial_transfer_end_callback(GB_gameboy_t *gb, GB_serial_transfer_end_callback_t callback);
+
+/* These APIs are used when using external clock */
+uint8_t GB_serial_get_data(GB_gameboy_t *gb);
+void GB_serial_set_data(GB_gameboy_t *gb, uint8_t data);
+
 #endif /* GB_h */
diff --git a/Core/memory.c b/Core/memory.c
index 0ea1330..ecc9e54 100644
--- a/Core/memory.c
+++ b/Core/memory.c
@@ -576,6 +576,9 @@ static void write_high_memory(GB_gameboy_t *gb, uint16_t addr, uint8_t value)
                 gb->io_registers[GB_IO_SC] = value | (~0x83);
                 if ((value & 0x80) && (value & 0x1) ) {
                     gb->serial_cycles = gb->cgb_mode && (value & 2)? 128 : 4096;
+                    if (gb->serial_transfer_start_callback) {
+                        gb->serial_transfer_start_callback(gb, gb->io_registers[GB_IO_SB]);
+                    }
                 }
                 else {
                     gb->serial_cycles = 0;
diff --git a/Core/timing.c b/Core/timing.c
index 0e6a2a2..c1f8ebc 100644
--- a/Core/timing.c
+++ b/Core/timing.c
@@ -45,7 +45,14 @@ void GB_advance_cycles(GB_gameboy_t *gb, uint8_t cycles)
         if (gb->serial_cycles <= cycles) {
             gb->serial_cycles = 0;
             gb->io_registers[GB_IO_SC] &= ~0x80;
-            gb->io_registers[GB_IO_SB] = 0xFF;
+            /* TODO: Does SB "update" bit by bit? */
+            if (gb->serial_transfer_end_callback) {
+                gb->io_registers[GB_IO_SB] = gb->serial_transfer_end_callback(gb);
+            }
+            else {
+                gb->io_registers[GB_IO_SB] = 0xFF;
+            }
+            
             gb->io_registers[GB_IO_IF] |= 8;
         }
         else {