diff --git a/cores/arduino/HardwareSerial.h b/cores/arduino/HardwareSerial.h
index 7c3a76ad2..62508e786 100644
--- a/cores/arduino/HardwareSerial.h
+++ b/cores/arduino/HardwareSerial.h
@@ -68,7 +68,7 @@ class HardwareSerial : public Stream
 {
   public:
     virtual void begin(unsigned long);
-    virtual void begin(unsigned long baudrate, uint8_t config);
+    virtual void begin(unsigned long baudrate, uint16_t config);
     virtual void end();
     virtual int available(void) = 0;
     virtual int peek(void) = 0;
diff --git a/cores/arduino/SERCOM.cpp b/cores/arduino/SERCOM.cpp
index 34d3aa18b..5aa52e510 100644
--- a/cores/arduino/SERCOM.cpp
+++ b/cores/arduino/SERCOM.cpp
@@ -62,9 +62,9 @@ void SERCOM::initUART(SercomUartMode mode, SercomUartSampleRate sampleRate, uint
     }
 
     // Asynchronous arithmetic mode
-    // 65535 * ( 1 - sampleRateValue * baudrate / SystemCoreClock);
-    // 65535 - 65535 * (sampleRateValue * baudrate / SystemCoreClock));
-    sercom->USART.BAUD.reg = 65535.0f * ( 1.0f - (float)(sampleRateValue) * (float)(baudrate) / (float)(SystemCoreClock));
+    // 65536 * ( 1 - sampleRateValue * baudrate / SystemCoreClock);
+    // add 0.5 to round up/down as appropriate
+    sercom->USART.BAUD.reg = 65536.0f * ( 1.0f - (float)(sampleRateValue) * (float)(baudrate) / (float)(SystemCoreClock)) + 0.5f;
   }
 }
 void SERCOM::initFrame(SercomUartCharSize charSize, SercomDataOrder dataOrder, SercomParityMode parityMode, SercomNumberStopBit nbStopBits)
@@ -112,7 +112,7 @@ void SERCOM::enableUART()
 void SERCOM::flushUART()
 {
   // Wait for transmission to complete
-  while(sercom->USART.INTFLAG.bit.DRE != SERCOM_USART_INTFLAG_DRE);
+  while(!sercom->USART.INTFLAG.bit.TXC);
 }
 
 void SERCOM::clearStatusUART()
@@ -168,8 +168,8 @@ uint8_t SERCOM::readDataUART()
 
 int SERCOM::writeDataUART(uint8_t data)
 {
-  //Flush UART buffer
-  flushUART();
+  // Wait for data register to be empty
+  while(!isDataRegisterEmptyUART());
 
   //Put data into DATA register
   sercom->USART.DATA.reg = (uint16_t)data;
diff --git a/cores/arduino/Uart.cpp b/cores/arduino/Uart.cpp
index 6f24bed9e..7a718e2c1 100644
--- a/cores/arduino/Uart.cpp
+++ b/cores/arduino/Uart.cpp
@@ -34,7 +34,7 @@ void Uart::begin(unsigned long baudrate)
   begin(baudrate, (uint8_t)SERIAL_8N1);
 }
 
-void Uart::begin(unsigned long baudrate, uint8_t config)
+void Uart::begin(unsigned long baudrate, uint16_t config)
 {
   pinPeripheral(uc_pinRX, g_APinDescription[uc_pinRX].ulPinType);
   pinPeripheral(uc_pinTX, g_APinDescription[uc_pinTX].ulPinType);
@@ -93,7 +93,7 @@ size_t Uart::write(const uint8_t data)
   return 1;
 }
 
-SercomNumberStopBit Uart::extractNbStopBit(uint8_t config)
+SercomNumberStopBit Uart::extractNbStopBit(uint16_t config)
 {
   switch(config & HARDSER_STOP_BIT_MASK)
   {
@@ -106,7 +106,7 @@ SercomNumberStopBit Uart::extractNbStopBit(uint8_t config)
   }
 }
 
-SercomUartCharSize Uart::extractCharSize(uint8_t config)
+SercomUartCharSize Uart::extractCharSize(uint16_t config)
 {
   switch(config & HARDSER_DATA_MASK)
   {
@@ -126,7 +126,7 @@ SercomUartCharSize Uart::extractCharSize(uint8_t config)
   }
 }
 
-SercomParityMode Uart::extractParity(uint8_t config)
+SercomParityMode Uart::extractParity(uint16_t config)
 {
   switch(config & HARDSER_PARITY_MASK)
   {
diff --git a/cores/arduino/Uart.h b/cores/arduino/Uart.h
index 3c88d6711..7115da740 100644
--- a/cores/arduino/Uart.h
+++ b/cores/arduino/Uart.h
@@ -29,7 +29,7 @@ class Uart : public HardwareSerial
   public:
     Uart(SERCOM *_s, uint8_t _pinRX, uint8_t _pinTX, SercomRXPad _padRX, SercomUartTXPad _padTX);
     void begin(unsigned long baudRate);
-    void begin(unsigned long baudrate, uint8_t config);
+    void begin(unsigned long baudrate, uint16_t config);
     void end();
     int available();
     int peek();
@@ -51,7 +51,7 @@ class Uart : public HardwareSerial
     SercomRXPad uc_padRX;
     SercomUartTXPad uc_padTX;
 
-    SercomNumberStopBit extractNbStopBit(uint8_t config);
-    SercomUartCharSize extractCharSize(uint8_t config);
-    SercomParityMode extractParity(uint8_t config);
+    SercomNumberStopBit extractNbStopBit(uint16_t config);
+    SercomUartCharSize extractCharSize(uint16_t config);
+    SercomParityMode extractParity(uint16_t config);
 };