diff --git a/IO_Modbus.cpp b/IO_Modbus.cpp
index 7942bb7..160236c 100644
--- a/IO_Modbus.cpp
+++ b/IO_Modbus.cpp
@@ -171,7 +171,7 @@ uint16_t div8RndUp(uint16_t value) {
   return (value + 7) >> 3;
 }
 
-ModbusRTUComm::ModbusRTUComm(Stream& serial, int8_t dePin, int8_t rePin) : _serial(serial) {
+ModbusRTUComm::ModbusRTUComm(Stream& serial, VPIN dePin, VPIN rePin) : _serial(serial) {
   _dePin = dePin;
   _rePin = rePin;
 }
@@ -204,13 +204,13 @@ void ModbusRTUComm::begin(unsigned long baud, uint32_t config) {
   #if defined(ARDUINO_UNOR4_MINIMA) || defined(ARDUINO_UNOR4_WIFI) || defined(ARDUINO_GIGA) || (defined(ARDUINO_NANO_RP2040_CONNECT) && defined(ARDUINO_ARCH_MBED))
   _postDelay = ((bitsPerChar * 1000000) / baud) + 2;
   #endif
-  if (_dePin >= 0) {
+  if (_dePin != VPIN_NONE) {
     pinMode(_dePin, OUTPUT);
-    digitalWrite(_dePin, LOW);
+    ArduinoPins::fastWriteDigital(_dePin, LOW);
   }
-  if (_rePin >= 0) {
+  if (_rePin != VPIN_NONE) {
     pinMode(_rePin, OUTPUT);
-    digitalWrite(_rePin, LOW);
+    ArduinoPins::fastWriteDigital(_rePin, LOW);
   }
   clearRxBuffer();
 }
@@ -249,13 +249,13 @@ ModbusRTUCommError ModbusRTUComm::readAdu(ModbusADU& adu) {
 
 void ModbusRTUComm::writeAdu(ModbusADU& adu) {
   adu.updateCrc();
-  if (_dePin >= 0) digitalWrite(_dePin, HIGH);
-  if (_rePin >= 0) digitalWrite(_rePin, HIGH);
+  if (_dePin != VPIN_NONE) ArduinoPins::fastWriteDigital(_dePin, HIGH);
+  if (_rePin != VPIN_NONE) ArduinoPins::fastWriteDigital(_rePin, HIGH);
   _serial.write(adu.rtu, adu.getRtuLen());
   _serial.flush();
-  ///delayMicroseconds(_postDelay);
-  if (_dePin >= 0) digitalWrite(_dePin, LOW);
-  if (_rePin >= 0) digitalWrite(_rePin, LOW);
+  //delayMicroseconds(_postDelay);
+  if (_dePin != VPIN_NONE) ArduinoPins::fastWriteDigital(_dePin, LOW);
+  if (_rePin != VPIN_NONE) ArduinoPins::fastWriteDigital(_rePin, LOW);
 }
 
 void ModbusRTUComm::clearRxBuffer() {
@@ -268,49 +268,43 @@ void ModbusRTUComm::clearRxBuffer() {
   } while (micros() - startMicros < _frameTimeout);
 }
 
-ModbusRTUMaster::ModbusRTUMaster(Stream& serial, int8_t dePin, int8_t rePin) : _rtuComm(serial, dePin, rePin) {
-  _rtuComm.setTimeout(500);
-}
 
-void ModbusRTUMaster::setTimeout(unsigned long timeout) {
+void Modbus::setTimeout(unsigned long timeout) {
   _rtuComm.setTimeout(timeout);
 }
 
-void ModbusRTUMaster::begin(unsigned long baud, uint32_t config) {
-  _rtuComm.begin(baud, config);
-}
 
 
 
-ModbusRTUMasterError ModbusRTUMaster::readCoils(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity) {
+ModbusRTUMasterError Modbus::readCoils(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity) {
   return _readValues(id, 1, startAddress, buf, quantity);
 }
 
-ModbusRTUMasterError ModbusRTUMaster::readDiscreteInputs(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity) {
+ModbusRTUMasterError Modbus::readDiscreteInputs(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity) {
   return _readValues(id, 2, startAddress, buf, quantity);
 }
 
-ModbusRTUMasterError ModbusRTUMaster::readHoldingRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity) {
+ModbusRTUMasterError Modbus::readHoldingRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity) {
   return _readValues(id, 3, startAddress, buf, quantity);
 }
 
-ModbusRTUMasterError ModbusRTUMaster::readInputRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity) {
+ModbusRTUMasterError Modbus::readInputRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity) {
   return _readValues(id, 4, startAddress, buf, quantity);
 }
 
 
 
-ModbusRTUMasterError ModbusRTUMaster::writeSingleCoil(uint8_t id, uint16_t address, char value) {
+ModbusRTUMasterError Modbus::writeSingleCoil(uint8_t id, uint16_t address, char value) {
   return _writeSingleValue(id, 5, address, ((value) ? 0xFF00 : 0x0000));
 }
 
-ModbusRTUMasterError ModbusRTUMaster::writeSingleHoldingRegister(uint8_t id, uint16_t address, uint16_t value) {
+ModbusRTUMasterError Modbus::writeSingleHoldingRegister(uint8_t id, uint16_t address, uint16_t value) {
   return _writeSingleValue(id, 6, address, value);
 }
 
 
 
-ModbusRTUMasterError ModbusRTUMaster::writeMultipleCoils(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity) {
+ModbusRTUMasterError Modbus::writeMultipleCoils(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity) {
   const uint8_t functionCode = 15;
   if (id > 247) return MODBUS_RTU_MASTER_INVALID_ID;
   if (!buf) return MODBUS_RTU_MASTER_INVALID_BUFFER;
@@ -345,7 +339,7 @@ ModbusRTUMasterError ModbusRTUMaster::writeMultipleCoils(uint8_t id, uint16_t st
   return MODBUS_RTU_MASTER_SUCCESS;
 }
 
-ModbusRTUMasterError ModbusRTUMaster::writeMultipleHoldingRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity) {
+ModbusRTUMasterError Modbus::writeMultipleHoldingRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity) {
   uint8_t functionCode = 16;
   if (id > 247) return MODBUS_RTU_MASTER_INVALID_ID;
   if (!buf) return MODBUS_RTU_MASTER_INVALID_BUFFER;
@@ -379,13 +373,13 @@ ModbusRTUMasterError ModbusRTUMaster::writeMultipleHoldingRegisters(uint8_t id,
 
 
 
-uint8_t ModbusRTUMaster::getExceptionResponse() {
+uint8_t Modbus::getExceptionResponse() {
   return _exceptionResponse;
 }
 
 
 
-ModbusRTUMasterError ModbusRTUMaster::_readValues(uint8_t id, uint8_t functionCode, uint16_t startAddress, char buf[], uint16_t quantity) {
+ModbusRTUMasterError Modbus::_readValues(uint8_t id, uint8_t functionCode, uint16_t startAddress, char buf[], uint16_t quantity) {
   if (id < 1 || id > 247) return MODBUS_RTU_MASTER_INVALID_ID;
   if (!buf) return MODBUS_RTU_MASTER_INVALID_BUFFER;
   if (quantity == 0 || quantity > 2000) return MODBUS_RTU_MASTER_INVALID_QUANTITY;
@@ -413,7 +407,7 @@ ModbusRTUMasterError ModbusRTUMaster::_readValues(uint8_t id, uint8_t functionCo
   return MODBUS_RTU_MASTER_SUCCESS;
 }
 
-ModbusRTUMasterError ModbusRTUMaster::_readValues(uint8_t id, uint8_t functionCode, uint16_t startAddress, uint16_t buf[], uint16_t quantity) {
+ModbusRTUMasterError Modbus::_readValues(uint8_t id, uint8_t functionCode, uint16_t startAddress, uint16_t buf[], uint16_t quantity) {
   if (id < 1 || id > 247) return MODBUS_RTU_MASTER_INVALID_ID;
   if (!buf) return MODBUS_RTU_MASTER_INVALID_BUFFER;
   if (quantity == 0 || quantity > 125) return MODBUS_RTU_MASTER_INVALID_QUANTITY;
@@ -441,7 +435,7 @@ ModbusRTUMasterError ModbusRTUMaster::_readValues(uint8_t id, uint8_t functionCo
   return MODBUS_RTU_MASTER_SUCCESS;
 }
 
-ModbusRTUMasterError ModbusRTUMaster::_writeSingleValue(uint8_t id, uint8_t functionCode, uint16_t address, uint16_t value) {
+ModbusRTUMasterError Modbus::_writeSingleValue(uint8_t id, uint8_t functionCode, uint16_t address, uint16_t value) {
   if (id > 247) return MODBUS_RTU_MASTER_INVALID_ID;
   ModbusADU adu;
   adu.setUnitId(id);
@@ -467,7 +461,7 @@ ModbusRTUMasterError ModbusRTUMaster::_writeSingleValue(uint8_t id, uint8_t func
 
 
 
-ModbusRTUMasterError ModbusRTUMaster::_translateCommError(ModbusRTUCommError commError) {
+ModbusRTUMasterError Modbus::_translateCommError(ModbusRTUCommError commError) {
   switch (commError) {
     case MODBUS_RTU_COMM_SUCCESS:
       return MODBUS_RTU_MASTER_SUCCESS;
@@ -488,12 +482,13 @@ ModbusRTUMasterError ModbusRTUMaster::_translateCommError(ModbusRTUCommError com
 
 
 // Constructor for Modbus
-Modbus::Modbus(uint8_t busNo, HardwareSerial serial, unsigned long baud, uint16_t cycleTimeMS, int8_t _dePin) {
-  
-  //serial.write("\002\004",2);
-  ModbusRTUMaster _modbusmaster(serial, _dePin);
+Modbus::Modbus(uint8_t busNo, HardwareSerial &serial, unsigned long baud, uint16_t cycleTimeMS, int8_t txPin) : _rtuComm(serial, txPin) {
   _baud = baud;
   _serialD = &serial;
+  _txPin = txPin;
+  _rtuComm.setTimeout(500);
+  
+  
   _busNo = busNo;
   _cycleTime = cycleTimeMS * 1000UL; // convert from milliseconds to microseconds.
   //if (_transmitEnablePin != VPIN_NONE) {
@@ -505,9 +500,9 @@ Modbus::Modbus(uint8_t busNo, HardwareSerial serial, unsigned long baud, uint16_
   //_modbusmaster.begin(baud);
   //DIAG(F("ModbusInit: %d %d"), _transmitEnablePin, _baud);
   // Add device to HAL device chain
-  serial.begin(baud, SERIAL_8N1);
+  
   IODevice::addDevice(this);
-  _modbusmaster.begin(baud, SERIAL_8N1);
+  
   // Add bus to CMRIbus chain.
   _nextBus = _busList;
   _busList = this;
@@ -534,16 +529,16 @@ void Modbus::_loop(unsigned long currentMicros) {
   const char* errorStrings[16] = { "success", "invalid id", "invalid buffer", "invalid quantity", "response timeout", "frame error", "crc error", "unknown comm error", "unexpected id", "exception response", "unexpected function code", "unexpected response length", "unexpected byte count", "unexpected address", "unexpected value", "unexpected quantity" };
   
   uint8_t error;
-  //error = _modbusmaster->writeMultipleHoldingRegisters(_currentNode->getNodeID(), 0, (uint16_t*) _currentNode->holdingRegisters, _currentNode->getNumHoldingRegisters());
+  error = writeMultipleHoldingRegisters(_currentNode->getNodeID(), 0, (uint16_t*) _currentNode->holdingRegisters, _currentNode->getNumHoldingRegisters());
   DIAG(F("ModbusHR: T%d F%d N%d %s"), _currentNode->getNodeID(), 0, _currentNode->getNumHoldingRegisters(), errorStrings[error]);
 
-  error = _modbusmaster->writeMultipleCoils(_currentNode->getNodeID(), 0, (char*) _currentNode->coils, _currentNode->getNumCoils());
+  error = writeMultipleCoils(_currentNode->getNodeID(), 0, (char*) _currentNode->coils, _currentNode->getNumCoils());
   DIAG(F("ModbusMC: T%d F%d N%d %s"), _currentNode->getNodeID(), 0, _currentNode->getNumCoils(), errorStrings[error]);
 
-  //error = _modbusmaster->readDiscreteInputs(_currentNode->getNodeID(), 0, (char*) _currentNode->discreteInputs, _currentNode->getNumDiscreteInputs());
+  error = readDiscreteInputs(_currentNode->getNodeID(), 0, (char*) _currentNode->discreteInputs, _currentNode->getNumDiscreteInputs());
   DIAG(F("ModbusDI: T%d F%d N%d %s"), _currentNode->getNodeID(), 0, _currentNode->getNumDiscreteInputs(), errorStrings[error]);
 
-  //error = _modbusmaster->readInputRegisters(_currentNode->getNodeID(), 0, (uint16_t*) _currentNode->inputRegisters, _currentNode->getNumInputRegisters());
+  error = readInputRegisters(_currentNode->getNodeID(), 0, (uint16_t*) _currentNode->inputRegisters, _currentNode->getNumInputRegisters());
   DIAG(F("ModbusIR: T%d F%d N%d %s"), _currentNode->getNodeID(), 0, _currentNode->getNumInputRegisters(), errorStrings[error]);
 
 
diff --git a/IO_Modbus.h b/IO_Modbus.h
index 6e64053..a8313ea 100644
--- a/IO_Modbus.h
+++ b/IO_Modbus.h
@@ -107,17 +107,17 @@ enum ModbusRTUCommError : uint8_t {
 
 class ModbusRTUComm {
   public:
-    ModbusRTUComm(Stream& serial, int8_t dePin = -1, int8_t rePin = -1);
+    ModbusRTUComm(Stream& serial, VPIN dePin = VPIN_NONE, VPIN rePin = VPIN_NONE);
     void begin(unsigned long baud, uint32_t config = SERIAL_8N1);
     void setTimeout(unsigned long timeout);
     ModbusRTUCommError readAdu(ModbusADU& adu);
     void writeAdu(ModbusADU& adu);
     void clearRxBuffer();
-
-  private:
     Stream& _serial;
-    int8_t _dePin;
-    int8_t _rePin;
+    VPIN _dePin;
+    VPIN _rePin;
+  private:
+    
     unsigned long _charTimeout;
     unsigned long _frameTimeout;
     unsigned long _postDelay = 0;
@@ -145,32 +145,16 @@ enum ModbusRTUMasterError : uint8_t {
 
 class ModbusRTUMaster {
   public:
-    ModbusRTUMaster(Stream& serial, int8_t dePin = -1, int8_t rePin = -1);
-    void setTimeout(unsigned long timeout);
+    ModbusRTUMaster(Stream& serial, VPIN dePin = VPIN_NONE, VPIN rePin = VPIN_NONE);
+    
     void begin(unsigned long baud, uint32_t config = SERIAL_8N1);
 
-    ModbusRTUMasterError readCoils(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity);
-    ModbusRTUMasterError readDiscreteInputs(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity);
-    ModbusRTUMasterError readHoldingRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity);
-    ModbusRTUMasterError readInputRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity);
+    
 
-    ModbusRTUMasterError writeSingleCoil(uint8_t id, uint16_t address, char value);
-    ModbusRTUMasterError writeSingleHoldingRegister(uint8_t id, uint16_t address, uint16_t value);
-    ModbusRTUMasterError writeMultipleCoils(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity);
-    ModbusRTUMasterError writeMultipleHoldingRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity);
-
-    uint8_t getExceptionResponse();
+    
 
   private:
-    ModbusRTUComm _rtuComm;
-    uint8_t _exceptionResponse = 0;
-
-    ModbusRTUMasterError _readValues(uint8_t id, uint8_t functionCode, uint16_t startAddress, char buf[], uint16_t quantity);
-    ModbusRTUMasterError _readValues(uint8_t id, uint8_t functionCode, uint16_t startAddress, uint16_t buf[], uint16_t quantity);
-    ModbusRTUMasterError _writeSingleValue(uint8_t id, uint8_t functionCode, uint16_t address, uint16_t value);
-
-    ModbusRTUMasterError _translateCommError(ModbusRTUCommError commError);
-
+    
 };
 
 
@@ -304,11 +288,14 @@ private:
   uint8_t _busNo;
 
   unsigned long _baud;
+  int8_t _txPin;
   Modbusnode *_nodeListStart = NULL, *_nodeListEnd = NULL;
   Modbusnode *_currentNode = NULL;
-  
+  uint8_t _exceptionResponse = 0;
+  uint8_t getExceptionResponse();
   uint16_t _receiveDataIndex = 0;  // Index of next data byte to be received.
   Modbus *_nextBus = NULL;  // Pointer to next bus instance in list.
+  void setTimeout(unsigned long timeout);
   unsigned long _cycleStartTime = 0;
   unsigned long _timeoutStart = 0;
   unsigned long _cycleTime; // target time between successive read/write cycles, microseconds
@@ -318,26 +305,39 @@ private:
   unsigned long _byteTransmitTime; // time in us for transmission of one byte
 
   static Modbus *_busList; // linked list of defined bus instances
-  
+  ModbusRTUMasterError _readValues(uint8_t id, uint8_t functionCode, uint16_t startAddress, char buf[], uint16_t quantity);
+  ModbusRTUMasterError _readValues(uint8_t id, uint8_t functionCode, uint16_t startAddress, uint16_t buf[], uint16_t quantity);
+  ModbusRTUMasterError _writeSingleValue(uint8_t id, uint8_t functionCode, uint16_t address, uint16_t value);
 public:
-  static void create(uint8_t busNo, HardwareSerial& serial, unsigned long baud, uint16_t cycleTimeMS=500, int8_t _dePin=0) {
-    new Modbus(busNo, serial, baud, cycleTimeMS, _dePin);
+  static void create(uint8_t busNo, HardwareSerial& serial, unsigned long baud, uint16_t cycleTimeMS=500, int8_t txPin=-1) {
+    new Modbus(busNo, serial, baud, cycleTimeMS, txPin);
   }
-  HardwareSerial *_serialD = nullptr;
-  ModbusRTUMaster *_modbusmaster;
-  
+  HardwareSerial *_serialD;
+  //ModbusRTUMaster *_modbusmaster;
+  ModbusRTUComm _rtuComm;
   // Device-specific initialisation
   void _begin() override {
     //ModbusRTUMaster _modbusmaster(*_serialD, _transmitEnablePin, -1);
-    
-    
+    _serialD->begin(_baud, SERIAL_8N1);
+    //ModbusRTUMaster _modbusmaster(*_serialD, _txPin, -1);
+    _rtuComm.begin(_baud, SERIAL_8N1);
+  
     //_serialD->println("test");
     
   #if defined(DIAG_IO)
     _display();
   #endif
   }
+  ModbusRTUMasterError _translateCommError(ModbusRTUCommError commError);
+  ModbusRTUMasterError readCoils(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity);
+  ModbusRTUMasterError readDiscreteInputs(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity);
+  ModbusRTUMasterError readHoldingRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity);
+  ModbusRTUMasterError readInputRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity);
 
+  ModbusRTUMasterError writeSingleCoil(uint8_t id, uint16_t address, char value);
+  ModbusRTUMasterError writeSingleHoldingRegister(uint8_t id, uint16_t address, uint16_t value);
+  ModbusRTUMasterError writeMultipleCoils(uint8_t id, uint16_t startAddress, char buf[], uint16_t quantity);
+  ModbusRTUMasterError writeMultipleHoldingRegisters(uint8_t id, uint16_t startAddress, uint16_t buf[], uint16_t quantity);
   // Loop function (overriding IODevice::_loop(unsigned long))
   void _loop(unsigned long currentMicros) override;
 
@@ -368,7 +368,7 @@ public:
   }
 
 protected:
-  Modbus(uint8_t busNo, HardwareSerial serial, unsigned long baud, uint16_t cycleTimeMS, int8_t _dePin);
+  Modbus(uint8_t busNo, HardwareSerial &serial, unsigned long baud, uint16_t cycleTimeMS, int8_t txPin);
 
 public: