diff --git a/libraries/mbed/common/I2C.cpp b/libraries/mbed/common/I2C.cpp
index bf2c3c3c81..8d4e48f0ac 100644
--- a/libraries/mbed/common/I2C.cpp
+++ b/libraries/mbed/common/I2C.cpp
@@ -52,9 +52,9 @@ int I2C::write(int address, const char* data, int length, bool repeated) {
     aquire();
 
     int stop = (repeated) ? 0 : 1;
-    int retval = i2c_write(&_i2c, address, data, length, stop);
+    int written = i2c_write(&_i2c, address, data, length, stop);
 
-    return retval;
+    return length != written;
 }
 
 int I2C::write(int data) {
@@ -66,9 +66,9 @@ int I2C::read(int address, char* data, int length, bool repeated) {
     aquire();
 
     int stop = (repeated) ? 0 : 1;
-    int retval = i2c_read(&_i2c, address, data, length, stop);
+    int read = i2c_read(&_i2c, address, data, length, stop);
 
-    return retval;
+    return length != read;
 }
 
 int I2C::read(int ack) {
diff --git a/libraries/mbed/common/I2CSlave.cpp b/libraries/mbed/common/I2CSlave.cpp
index 43ee3f1fa2..3db7f52589 100644
--- a/libraries/mbed/common/I2CSlave.cpp
+++ b/libraries/mbed/common/I2CSlave.cpp
@@ -39,7 +39,7 @@ int I2CSlave::receive(void) {
 }
 
 int I2CSlave::read(char *data, int length) {
-    return i2c_slave_read(&_i2c, data, length);
+    return i2c_slave_read(&_i2c, data, length) != length;
 }
 
 int I2CSlave::read(void) {
@@ -47,7 +47,7 @@ int I2CSlave::read(void) {
 }
 
 int I2CSlave::write(const char *data, int length) {
-    return i2c_slave_write(&_i2c, data, length);
+    return i2c_slave_write(&_i2c, data, length) != length;
 }
 
 int I2CSlave::write(int data) {
diff --git a/libraries/mbed/hal/i2c_api.h b/libraries/mbed/hal/i2c_api.h
index f0bbaaef43..5682e29425 100644
--- a/libraries/mbed/hal/i2c_api.h
+++ b/libraries/mbed/hal/i2c_api.h
@@ -26,6 +26,11 @@ extern "C" {
 
 typedef struct i2c_s i2c_t;
 
+enum {
+  I2C_ERROR_NO_SLAVE = -1,
+  I2C_ERROR_BUS_BUSY = -2
+};
+
 void i2c_init         (i2c_t *obj, PinName sda, PinName scl);
 void i2c_frequency    (i2c_t *obj, int hz);
 int  i2c_start        (i2c_t *obj);
diff --git a/libraries/mbed/targets/hal/Freescale/TARGET_KL25Z/i2c_api.c b/libraries/mbed/targets/hal/Freescale/TARGET_KL25Z/i2c_api.c
index c7feee8bc8..3dc24dd3c6 100644
--- a/libraries/mbed/targets/hal/Freescale/TARGET_KL25Z/i2c_api.c
+++ b/libraries/mbed/targets/hal/Freescale/TARGET_KL25Z/i2c_api.c
@@ -221,12 +221,12 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
 
     if (i2c_start(obj)) {
         i2c_stop(obj);
-        return 1;
+        return I2C_ERROR_BUS_BUSY;
     }
 
     if (i2c_do_write(obj, (address | 0x01))) {
         i2c_stop(obj);
-        return 1;
+        return I2C_ERROR_NO_SLAVE;
     }
 
     // set rx mode
@@ -238,7 +238,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         uint8_t stop_ = (count == (length - 1)) ? 1 : 0;
         if (i2c_do_read(obj, ptr, stop_)) {
             i2c_stop(obj);
-            return 1;
+            return count;
         }
     }
 
@@ -250,25 +250,25 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     // last read
     data[count-1] = obj->i2c->D;
 
-    return 0;
+    return length;
 }
 int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
     int i;
 
     if (i2c_start(obj)) {
         i2c_stop(obj);
-        return 1;
+        return I2C_ERROR_BUS_BUSY;
     }
 
     if (i2c_do_write(obj, (address & 0xFE))) {
         i2c_stop(obj);
-        return 1;
+        return I2C_ERROR_NO_SLAVE;
     }
 
     for (i = 0; i < length; i++) {
         if(i2c_do_write(obj, data[i])) {
             i2c_stop(obj);
-            return 1;
+            return i;
         }
     }
 
@@ -276,7 +276,7 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
         i2c_stop(obj);
     }
 
-    return 0;
+    return length;
 }
 
 void i2c_reset(i2c_t *obj) {
@@ -363,7 +363,7 @@ int i2c_slave_read(i2c_t *obj, char *data, int length) {
     for (count = 0; count < (length - 1); count++) {
         data[count] = obj->i2c->D;
         if(i2c_wait_end_rx_transfer(obj)) {
-            return 0;
+            return count;
         }
     }
 
@@ -382,7 +382,7 @@ int i2c_slave_write(i2c_t *obj, const char *data, int length) {
     
     for (i = 0; i < length; i++) {
         if(i2c_do_write(obj, data[count++]) == 2) {
-            return 0;
+            return i;
         }
     }
     
@@ -393,7 +393,7 @@ int i2c_slave_write(i2c_t *obj, const char *data, int length) {
     // otherwise the master cannot generate a stop bit
     obj->i2c->D;
     if(i2c_wait_end_rx_transfer(obj) == 2) {
-        return 0;
+        return count;
     }
     
     return count;
diff --git a/libraries/mbed/targets/hal/NXP/TARGET_LPC11UXX/i2c_api.c b/libraries/mbed/targets/hal/NXP/TARGET_LPC11UXX/i2c_api.c
index 5f6a759212..aeca856e65 100644
--- a/libraries/mbed/targets/hal/NXP/TARGET_LPC11UXX/i2c_api.c
+++ b/libraries/mbed/targets/hal/NXP/TARGET_LPC11UXX/i2c_api.c
@@ -196,13 +196,13 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     
     if ((status != 0x10) && (status != 0x08)) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_BUS_BUSY;
     }
     
     status = i2c_do_write(obj, (address | 0x01), 1);
     if (status != 0x40) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
 
     // Read in all except last byte
@@ -211,7 +211,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         status = i2c_status(obj);
         if (status != 0x50) {
             i2c_stop(obj);
-            return status;
+            return count;
         }
         data[count] = (char) value;
     }
@@ -221,7 +221,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     status = i2c_status(obj);
     if (status != 0x58) {
         i2c_stop(obj);
-        return status;
+        return length - 1;
     }
     
     data[count] = (char) value;
@@ -231,7 +231,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         i2c_stop(obj);
     }
     
-    return 0;
+    return length;
 }
 
 int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
@@ -241,20 +241,20 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
     
     if ((status != 0x10) && (status != 0x08)) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_BUS_BUSY;
     }
     
     status = i2c_do_write(obj, (address & 0xFE), 1);
     if (status != 0x18) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     for (i=0; i<length; i++) {
         status = i2c_do_write(obj, data[i], 0);
         if(status != 0x28) {
             i2c_stop(obj);
-            return status;
+            return i;
         }
     }
     
@@ -265,7 +265,7 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
         i2c_stop(obj);
     }
     
-    return 0;
+    return length;
 }
 
 void i2c_reset(i2c_t *obj) {
@@ -343,7 +343,7 @@ int i2c_slave_read(i2c_t *obj, char *data, int length) {
     
     i2c_clear_SI(obj);
     
-    return (count - 1);
+    return count;
 }
 
 int i2c_slave_write(i2c_t *obj, const char *data, int length) {
diff --git a/libraries/mbed/targets/hal/NXP/TARGET_LPC176X/i2c_api.c b/libraries/mbed/targets/hal/NXP/TARGET_LPC176X/i2c_api.c
index 1730192539..102cabcbdb 100644
--- a/libraries/mbed/targets/hal/NXP/TARGET_LPC176X/i2c_api.c
+++ b/libraries/mbed/targets/hal/NXP/TARGET_LPC176X/i2c_api.c
@@ -204,13 +204,13 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     
     if ((status != 0x10) && (status != 0x08)) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_BUS_BUSY;
     }
     
     status = i2c_do_write(obj, (address | 0x01), 1);
     if (status != 0x40) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     // Read in all except last byte
@@ -219,7 +219,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         status = i2c_status(obj);
         if (status != 0x50) {
             i2c_stop(obj);
-            return status;
+            return count;
         }
         data[count] = (char) value;
     }
@@ -229,7 +229,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     status = i2c_status(obj);
     if (status != 0x58) {
         i2c_stop(obj);
-        return status;
+        return length - 1;
     }
     
     data[count] = (char) value;
@@ -239,7 +239,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         i2c_stop(obj);
     }
     
-    return 0;
+    return length;
 }
 
 int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
@@ -249,20 +249,20 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
     
     if ((status != 0x10) && (status != 0x08)) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_BUS_BUSY;
     }
     
     status = i2c_do_write(obj, (address & 0xFE), 1);
     if (status != 0x18) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     for (i=0; i<length; i++) {
         status = i2c_do_write(obj, data[i], 0);
         if(status != 0x28) {
             i2c_stop(obj);
-            return status;
+            return i;
         }
     }
     
@@ -273,7 +273,7 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
         i2c_stop(obj);
     }
     
-    return 0;
+    return length;
 }
 
 void i2c_reset(i2c_t *obj) {
@@ -351,7 +351,7 @@ int i2c_slave_read(i2c_t *obj, char *data, int length) {
     
     i2c_clear_SI(obj);
     
-    return (count - 1);
+    return count;
 }
 
 int i2c_slave_write(i2c_t *obj, const char *data, int length) {
diff --git a/libraries/mbed/targets/hal/NXP/TARGET_LPC23XX/i2c_api.c b/libraries/mbed/targets/hal/NXP/TARGET_LPC23XX/i2c_api.c
index b79c8fd1f2..79d290d262 100644
--- a/libraries/mbed/targets/hal/NXP/TARGET_LPC23XX/i2c_api.c
+++ b/libraries/mbed/targets/hal/NXP/TARGET_LPC23XX/i2c_api.c
@@ -203,13 +203,13 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     
     if ((status != 0x10) && (status != 0x08)) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_BUS_BUSY;
     }
     
     status = i2c_do_write(obj, (address | 0x01), 1);
     if (status != 0x40) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     // Read in all except last byte
@@ -218,7 +218,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         status = i2c_status(obj);
         if (status != 0x50) {
             i2c_stop(obj);
-            return status;
+            return count;
         }
         data[count] = (char) value;
     }
@@ -228,7 +228,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     status = i2c_status(obj);
     if (status != 0x58) {
         i2c_stop(obj);
-        return status;
+        return length - 1;
     }
     
     data[count] = (char) value;
@@ -238,7 +238,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         i2c_stop(obj);
     }
     
-    return 0;
+    return length;
 }
 
 int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
@@ -248,20 +248,20 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
     
     if ((status != 0x10) && (status != 0x08)) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_BUS_BUSY;
     }
     
     status = i2c_do_write(obj, (address & 0xFE), 1);
     if (status != 0x18) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     for (i=0; i<length; i++) {
         status = i2c_do_write(obj, data[i], 0);
         if (status != 0x28) {
             i2c_stop(obj);
-            return status;
+            return i;
         }
     }
     
@@ -272,7 +272,7 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
         i2c_stop(obj);
     }
     
-    return 0;
+    return length;
 }
 
 void i2c_reset(i2c_t *obj) {
@@ -353,7 +353,7 @@ int i2c_slave_read(i2c_t *obj, char *data, int length) {
     
     i2c_clear_SI(obj);
     
-    return (count - 1);
+    return count;
 }
 
 int i2c_slave_write(i2c_t *obj, const char *data, int length) {
diff --git a/libraries/mbed/targets/hal/NXP/TARGET_LPC408X/i2c_api.c b/libraries/mbed/targets/hal/NXP/TARGET_LPC408X/i2c_api.c
index ec5ace1229..d21a2c21db 100644
--- a/libraries/mbed/targets/hal/NXP/TARGET_LPC408X/i2c_api.c
+++ b/libraries/mbed/targets/hal/NXP/TARGET_LPC408X/i2c_api.c
@@ -213,13 +213,13 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     
     if ((status != 0x10) && (status != 0x08)) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_BUS_BUSY;
     }
     
     status = i2c_do_write(obj, (address | 0x01), 1);
     if (status != 0x40) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     // Read in all except last byte
@@ -228,7 +228,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         status = i2c_status(obj);
         if (status != 0x50) {
             i2c_stop(obj);
-            return status;
+            return count;
         }
         data[count] = (char) value;
     }
@@ -238,7 +238,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     status = i2c_status(obj);
     if (status != 0x58) {
         i2c_stop(obj);
-        return status;
+        return length - 1;
     }
     
     data[count] = (char) value;
@@ -248,7 +248,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         i2c_stop(obj);
     }
     
-    return 0;
+    return length;
 }
 
 int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
@@ -258,20 +258,20 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
     
     if ((status != 0x10) && (status != 0x08)) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_BUS_BUSY;
     }
     
     status = i2c_do_write(obj, (address & 0xFE), 1);
     if (status != 0x18) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     for (i=0; i<length; i++) {
         status = i2c_do_write(obj, data[i], 0);
         if (status != 0x28) {
             i2c_stop(obj);
-            return status;
+            return i;
         }
     }
     
@@ -282,7 +282,7 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
         i2c_stop(obj);
     }
     
-    return 0;
+    return length;
 }
 
 void i2c_reset(i2c_t *obj) {
@@ -363,7 +363,7 @@ int i2c_slave_read(i2c_t *obj, char *data, int length) {
     
     i2c_clear_SI(obj);
     
-    return (count - 1);
+    return count;
 }
 
 int i2c_slave_write(i2c_t *obj, const char *data, int length) {
diff --git a/libraries/mbed/targets/hal/NXP/TARGET_LPC81X/i2c_api.c b/libraries/mbed/targets/hal/NXP/TARGET_LPC81X/i2c_api.c
index 3a0c2a2583..d349d8917c 100644
--- a/libraries/mbed/targets/hal/NXP/TARGET_LPC81X/i2c_api.c
+++ b/libraries/mbed/targets/hal/NXP/TARGET_LPC81X/i2c_api.c
@@ -147,7 +147,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     status = i2c_do_write(obj, (address | 0x01), 1);
     if (status != 0x01) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     // Read in all except last byte
@@ -156,7 +156,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         status = i2c_status(obj);
         if (status != 0x00) {
             i2c_stop(obj);
-            return status;
+            return count;
         }
         data[count] = (char) value;
     }
@@ -166,7 +166,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
     status = i2c_status(obj);
     if (status != 0x01) {
         i2c_stop(obj);
-        return status;
+        return length - 1;
     }
     
     data[count] = (char) value;
@@ -178,7 +178,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         repeated_start = 1;
     }
     
-    return 0;
+    return length;
 }
 
 int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
@@ -189,14 +189,14 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
     status = i2c_do_write(obj, (address & 0xFE), 1);
     if (status != 0x02) {
         i2c_stop(obj);
-        return status;
+        return I2C_ERROR_NO_SLAVE;
     }
     
     for (i=0; i<length; i++) {
         status = i2c_do_write(obj, data[i], 0);
         if (status != 0x02) {
             i2c_stop(obj);
-            return status;
+            return i;
         }
     }
     
@@ -207,7 +207,7 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
         repeated_start = 1;
     }
     
-    return 0;
+    return length;
 }
 
 void i2c_reset(i2c_t *obj) {
diff --git a/libraries/mbed/targets/hal/STM/TARGET_STM32F4XX/i2c_api.c b/libraries/mbed/targets/hal/STM/TARGET_STM32F4XX/i2c_api.c
index c129b42a3e..1b8992786f 100644
--- a/libraries/mbed/targets/hal/STM/TARGET_STM32F4XX/i2c_api.c
+++ b/libraries/mbed/targets/hal/STM/TARGET_STM32F4XX/i2c_api.c
@@ -251,7 +251,7 @@ int i2c_read(i2c_t *obj, int address, char *data, int length, int stop) {
         i2c_stop(obj);
     }
 
-    return 0;
+    return length;
 }
 
 int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
@@ -273,7 +273,7 @@ int i2c_write(i2c_t *obj, int address, const char *data, int length, int stop) {
         i2c_stop(obj);
     }
 
-    return 0;
+    return length;
 }
 
 void i2c_reset(i2c_t *obj) {