diff --git a/cwSerialPort.cpp b/cwSerialPort.cpp
index b18b556..331109a 100644
--- a/cwSerialPort.cpp
+++ b/cwSerialPort.cpp
@@ -17,31 +17,52 @@ namespace cw
   {
     typedef struct port_str
     {
-      const char*           _deviceStr;
-      int                   _deviceH;
-      unsigned              _baudRate;
-      unsigned              _cfgFlags;
-      callbackFunc_t        _cbFunc;
-      void*                 _cbArg;
-      struct termios        _ttyAttrs;
-      struct pollfd         _pollfd;      
+      unsigned         _userId;
+      char*            _deviceStr;
+      int              _deviceH;
+      unsigned         _baudRate;
+      unsigned         _cfgFlags;
+      callbackFunc_t   _cbFunc;
+      void*            _cbArg;
+      struct termios   _ttyAttrs;
+      struct pollfd*   _pollfd;
+      struct port_str* _link;
     } port_t;
 
-    inline port_t* _portHandleToPtr(handle_t h){ return handleToPtr<handle_t,port_t>(h); }
-
-    void   _setClosedState( port_t* p )
+    typedef struct device_str
     {
-      if( p->_deviceStr != nullptr )
-        cw::mem::free(const_cast<char*>(p->_deviceStr));
-     
-      p->_deviceH = -1;
-      p->_deviceStr = nullptr;
-      p->_baudRate  = 0;
-      p->_cfgFlags  = 0;
-      p->_cbFunc    = nullptr;
-      p->_cbArg     = nullptr;
+      unsigned       _recvBufByteN;
+      void*          _recvBuf;
+      port_t*        _portL;
+      unsigned       _pollfdN;
+      struct pollfd* _pollfd;      
+    } device_t;
+
+    inline device_t* _handleToPtr(handle_t h)
+    { return handleToPtr<handle_t,device_t>(h); }
+
+    bool _isPortOpen( port_t* p )
+    { return p->_deviceH != -1; }
+
+    // Given a 'userId' return the assoc'd port record.
+    port_t* _idToPort( device_t* d, unsigned userId, bool errorFl = true )
+    {
+      port_t* p = d->_portL;
       
+      while( p != nullptr )
+      {
+        if( userId == p->_userId )
+          return p;
+        
+        p = p->_link;
+      }
+
+      if( errorFl )
+        cwLogError(kInvalidIdRC,"No port was found with id:%i.",userId);
+      
+      return nullptr;
     }
+
     
     rc_t _getAttributes( port_t* p, struct termios& attr ) 
     {
@@ -50,62 +71,179 @@ namespace cw
 
       return kOkRC;
     }
-    
-    rc_t _poll( port_t* p, unsigned timeOutMs )
+
+    // Called to read the serial device when data is known to be waiting.
+    rc_t _receive( device_t* d, port_t* p, unsigned& readN_Ref, void* buf=nullptr, unsigned bufByteN=0 )
+    {
+      rc_t     rc = kOkRC;
+      void*    b  = buf;
+      unsigned bN = bufByteN;
+      int      n  = 0;
+
+      readN_Ref = 0;
+     
+      
+      if( !_isPortOpen(p) )
+        return cwLogWarningRC( kResourceNotAvailableRC, "An attempt was made to read from a closed serial port.");
+      
+      
+      // if a buffer was not given
+      if( b ==nullptr || bufByteN == 0 )
+      {
+        b  = d->_recvBuf;
+        bN = d->_recvBufByteN;
+      }
+
+      // if attempt to read the port succeeded ...
+      if((n =read( p->_deviceH, b, bN )) != -1 )
+      {        
+        readN_Ref += n;
+
+        if( buf == nullptr || bufByteN == 0 )
+          p->_cbFunc( p->_cbArg, p->_userId, b, n );
+        
+      }
+      else
+      {
+        // ... or failed and it wasn't because the port was empty
+        if( errno != EAGAIN)
+          rc = cwLogSysError(kReadFailRC,errno,"An attempt to read the serial port '%s' failed.", p->_deviceStr );
+      }
+
+      return rc;
+    }
+
+
+    // Block devices waiting for data on a port. If userId is valid then wait for data on a specific port otherwise
+    // wait for data on all ports.
+    rc_t _poll( device_t* d, unsigned timeOutMs, unsigned& readN_Ref, unsigned userId=kInvalidId, void* buf=nullptr, unsigned bufByteN=0 )
     {
       rc_t rc = kOkRC;
       int sysRC;
 
-      if((sysRC = ::poll(&p->_pollfd,1,timeOutMs)) == 0)
+      readN_Ref = 0;
+
+      // if there are not ports then there is nothing to do
+      if( d->_pollfdN == 0 )
+        return rc;
+
+      struct pollfd* pfd  = d->_pollfd;   // first struct pollfd
+      unsigned       pfdN = d->_pollfdN;  // count of pollfd's
+      port_t*        p    = d->_portL;    // port assoc'd with first pollfd
+
+      // if only one port is to be read ...
+      if( userId != kInvalidId )
+      {
+        // ... then locate it
+        if((p    = _idToPort(d,userId)) == nullptr )
+          return kInvalidArgRC;
+        
+        pfd  = p->_pollfd;
+        pfdN = 1;
+      }
+
+      // A port to poll must exist
+      if( p == nullptr )
+        return cwLogError(kInvalidArgRC,"The port with id %i could not be found.",userId);
+      
+
+      // block waiting for data on one of the ports
+      if((sysRC = ::poll(pfd,pfdN,timeOutMs)) == 0)
         rc = kTimeOutRC;
       else
       {
+        // ::poll() encountered a system exception
         if( sysRC < 0 )
-          rc = cwLogSysError(kReadFailRC,errno,"Poll failed on serial port.");
+          return cwLogSysError(kReadFailRC,errno,"Poll failed on serial port.");
+
+        // interate through the ports looking for the ones which have data waiting ...
+        for(unsigned i=0; p!=nullptr; p=p->_link,++i)
+          if( p->_pollfd->revents & POLLIN )
+            // ... then read the data
+            if((rc = _receive( d, p, readN_Ref, buf, bufByteN )) != kOkRC )
+                return rc;
+        
       }
   
       return rc;
       
     }
-    
-    rc_t _destroy( port_t* p )
+
+    rc_t _closePort( device_t* d, port_t* p )
     {
       rc_t rc = kOkRC;
-      
-      // Block until all written output has been sent from the device.
-      // Note that this call is simply passed on to the serial device driver.
-      // See tcsendbreak(3) ("man 3 tcsendbreak") for details.
-      if (tcdrain(p->_deviceH) == -1)
-      {
-        rc = cwLogSysError(kFlushFailRC,errno,"Error waiting for serial device '%s' to drain.", p->_deviceStr );
-        goto errLabel;
-      }
 
-      // It is good practice to reset a serial port back to the state in
-      // which you found it. This is why we saved the original termios struct
-      // The constant TCSANOW (defined in termios.h) indicates that
-      // the change should take effect immediately.
-
-      if (tcsetattr(p->_deviceH, TCSANOW, &p->_ttyAttrs) ==  -1)
-      {
-        rc = cwLogSysError(kSetAttrFailRC,errno,"Error resetting tty attributes on serial device '%s'.",p->_deviceStr);
-        goto errLabel;
-      }
-	
+      // if the port is already closed
       if( p->_deviceH != -1 )
       {
+        // Block until all written output has been sent from the device.
+        // Note that this call is simply passed on to the serial device driver.
+        // See tcsendbreak(3) ("man 3 tcsendbreak") for details.
+        if (tcdrain(p->_deviceH) == -1)
+        {
+          rc = cwLogSysError(kFlushFailRC,errno,"Error waiting for serial device '%s' to drain.", p->_deviceStr );
+          goto errLabel;
+        }
+
+        // It is good practice to reset a serial port back to the state in
+        // which you found it. This is why we saved the original termios struct
+        // The constant TCSANOW (defined in termios.h) indicates that
+        // the change should take effect immediately.
+
+        if (tcsetattr(p->_deviceH, TCSANOW, &p->_ttyAttrs) ==  -1)
+        {
+          rc = cwLogSysError(kSetAttrFailRC,errno,"Error resetting tty attributes on serial device '%s'.",p->_deviceStr);
+          goto errLabel;
+        }
+	
         if( ::close(p->_deviceH ) != 0 )
         {
           rc = cwLogSysError(kCloseFailRC,errno,"Port close failed on serial dvice '%s'.", p->_deviceStr);
           goto errLabel;
         }
-		
-        _setClosedState(p);
+
       }
 
-      mem::release(p);
+
+      // reset the state of the port record
+      mem::release(p->_deviceStr);
+      p->_userId         = kInvalidId;
+      p->_deviceH        = -1;
+      p->_baudRate       = 0;
+      p->_cfgFlags       = 0;
+      p->_cbFunc         = nullptr;
+      p->_cbArg          = nullptr;
+      p->_pollfd->events = 0;
+      p->_pollfd->fd     = -1;
+      
 
     errLabel:
+      return rc;
+            
+    }
+
+    // Destroy the manager object.
+    rc_t _destroy( device_t* d )
+    {
+      rc_t    rc = kOkRC;
+      port_t* p  = d->_portL;
+      
+      while( p != nullptr )
+      {
+        port_t* p0 = p->_link;
+        
+        if((rc = _closePort(d,p)) != kOkRC )
+          return rc;
+
+        mem::release(p);
+        
+        p = p0;
+        
+      }
+
+      mem::release(d->_recvBuf);
+      mem::release(d);
+      
       return rc;      
     }
     
@@ -114,19 +252,90 @@ namespace cw
 }
 
 
-cw::rc_t cw::serialPort::create( handle_t& h, const char* deviceStr, unsigned baudRate, unsigned cfgFlags, callbackFunc_t cbFunc, void* cbArg )
+cw::rc_t cw::serialPort::create( handle_t& h, unsigned recvBufByteN )
 {
-  rc_t           rc = kOkRC;
-  struct termios options;
-
-  // if the port is already open then close it
+  rc_t rc;
   if((rc = destroy(h)) != kOkRC )
     return rc;
 
-  port_t* p = mem::allocZ<port_t>();
+  device_t* d = mem::allocZ<device_t>();
 
-  p->_deviceH = -1;
+  if( recvBufByteN > 0 )
+  {
+    d->_recvBuf      = mem::allocZ<uint8_t>( recvBufByteN );
+    d->_recvBufByteN = recvBufByteN;
+  }
+  
+  h.set(d);
+
+  return rc;
+}
+
+cw::rc_t cw::serialPort::destroy( handle_t& h )
+{
+  rc_t rc = kOkRC;
+  
+  if( !h.isValid() )
+    return rc;
+
+  device_t* d = _handleToPtr(h);
+
+  if((rc = _destroy(d)) != kOkRC )
+    return rc;
+
+  h.clear();
+  
+  return rc;
+}
+
+cw::rc_t cw::serialPort::createPort( handle_t h, unsigned userId, const char* deviceStr, unsigned baudRate, unsigned cfgFlags, callbackFunc_t cbFunc, void* cbArg )
+{
+  rc_t           rc = kOkRC;
+  device_t*      d  = _handleToPtr(h);
+  struct termios options;
+  port_t*        p;
+
+  // locate the port with the given user id
+  if((p = _idToPort(d,userId,false)) != nullptr )
+    if((rc = _closePort(d,p)) != kOkRC )
+      return rc;
+
+  // if a new port record must be allocated
+  if( p == nullptr )
+  {
+    unsigned portN = 0;
     
+    // look for an available port and count the number of existing ports
+    for(p=d->_portL; p!=nullptr; p=p->_link,++portN)
+      if( !_isPortOpen(p) )
+        break;
+
+    if( p == nullptr )
+    {
+      // allocate and link in the new port desc. record
+      p = mem::allocZ<port_t>();
+      p->_deviceH = -1;
+
+      // link in the new port as the first port
+      p->_link    = d->_portL;
+      d->_portL   = p;
+
+      // A new port has been allocated reallocate the pollfd array
+      mem::release(d->_pollfd);
+      d->_pollfdN = portN + 1;
+      d->_pollfd  = mem::allocZ<struct pollfd>(d->_pollfdN);
+
+      // link the port records to the their assoc'd pollfd record in d->_pollfd[]
+      port_t* pp = d->_portL;
+      for(unsigned i=0; pp!=nullptr; ++i,pp=pp->_link)
+      {
+        pp->_pollfd         = d->_pollfd + i;
+        pp->_pollfd->fd     = pp->_deviceH;
+        pp->_pollfd->events = POLLIN;
+      }
+    } 
+  }
+  
 	// open the port		
 	if( (p->_deviceH = ::open(deviceStr, O_RDWR | O_NOCTTY | O_NONBLOCK)) == -1 )
 	{
@@ -212,7 +421,6 @@ cw::rc_t cw::serialPort::create( handle_t& h, const char* deviceStr, unsigned ba
 
 	// set two stop bits    
   cwEnaBits( options.c_cflag, CSTOPB, cwIsFlag(cfgFlags, k2StopBitFl));
-    
     		    
   // set hardware flow control
   //cwEnaBits(options.c_cflag,		CCTS_OFLOW, 	cwIsFlag(cfgFlags, kCTS_OutFlowCtlFl)); 
@@ -230,41 +438,46 @@ cw::rc_t cw::serialPort::create( handle_t& h, const char* deviceStr, unsigned ba
   // Cause the new options to take effect immediately.
   if (tcsetattr(p->_deviceH, TCSANOW, &options) == -1)
   {
-
     rc = cwLogSysError(kSetAttrFailRC,errno,"Error setting tty attributes on serial device %.", deviceStr);
     goto errLabel;
   }
 
-  memset(&p->_pollfd,0,sizeof(p->_pollfd));
-  p->_pollfd.fd     = p->_deviceH;
-  p->_pollfd.events = POLLIN;
+  p->_userId         = userId;
+  p->_deviceStr      = cw::mem::allocStr( deviceStr );
+  p->_baudRate       = baudRate;
+	p->_cfgFlags       = cfgFlags;
+  p->_cbFunc         = cbFunc;
+  p->_cbArg          = cbArg;
+  p->_pollfd->fd     = p->_deviceH;
+  p->_pollfd->events = POLLIN;
   
-  p->_deviceStr = cw::mem::allocStr( deviceStr );
-  p->_baudRate  = baudRate;
-	p->_cfgFlags  = cfgFlags;
-  p->_cbFunc    = cbFunc;
-  p->_cbArg     = cbArg;
-
-  h.set(p);
+  h.set(d);
   
  errLabel:
   if( rc != kOkRC )
-    _destroy(p);
+    _closePort(d,p);
 				
   return rc;
   
 }
 
-cw::rc_t cw::serialPort::destroy(handle_t& h )
+cw::rc_t cw::serialPort::destroyPort(handle_t h, unsigned userId )
 {
   rc_t rc = kOkRC; 
   
-  if( !isopen(h) )
+  if( !isopen(h,userId) )
     return rc;
 
-  port_t* p = _portHandleToPtr(h);
+  device_t* d = _handleToPtr(h);
+  port_t*   p;
 
-  if((rc = _destroy(p)) != kOkRC )
+  // find the port to close
+  if((p = _idToPort(d,userId)) == nullptr )
+    return kInvalidArgRC;
+
+  // Close the selected port
+  // Note that closed ports are simply marked as closed (deviceH==-1) but not removed from the list.
+  if((rc = _closePort(d,p)) != kOkRC )
     return rc;
 
   h.clear();
@@ -272,26 +485,47 @@ cw::rc_t cw::serialPort::destroy(handle_t& h )
   return rc;
 }
 
-bool cw::serialPort::isopen( handle_t h)
+unsigned cw::serialPort::portCount( handle_t h )
 {
-  if( !h.isValid() )
-    return false;
-  
-  port_t* p = _portHandleToPtr(h);
-  return p->_deviceH != -1;
+  device_t* d = _handleToPtr(h);
+  return d->_pollfdN;  
 }
 
-cw::rc_t cw::serialPort::send( handle_t h, const void* byteA, unsigned byteN )
+unsigned cw::serialPort::portIndexToId( handle_t h, unsigned index )
 {
-  rc_t rc = kOkRC;
+  device_t* d = _handleToPtr(h);
+  unsigned i = 0;
+  for(port_t* p=d->_portL; p!=nullptr; p=p->_link,++i)
+    if( i == index )
+      return p->_userId;
+
+  return kInvalidId;
+}
+
+
+bool cw::serialPort::isopen( handle_t h, unsigned userId )
+{
+  device_t* d = _handleToPtr(h);
+  port_t*   p;
+  
+  if((p = _idToPort(d,userId)) == nullptr )
+    return false;
+
+  return _isPortOpen(p);  
+}
+
+cw::rc_t cw::serialPort::send( handle_t h, unsigned userId, const void* byteA, unsigned byteN )
+{
+  rc_t      rc = kOkRC;
+  device_t* d  = _handleToPtr(h);
+  port_t*   p;
 
-  port_t* p = _portHandleToPtr(h);
-      
-  if( !isopen(h)  )
-    return cwLogWarningRC( kResourceNotAvailableRC, "An attempt was made to transmit from a closed serial port.");
-        
   if( byteN == 0 )
     return rc;
+  
+  if((p = _idToPort(d,userId)) == nullptr )
+    return kInvalidArgRC;
+      
         
   // implement a non blocking write - if less than all the bytes were written then iterate
   unsigned i = 0;
@@ -314,92 +548,78 @@ cw::rc_t cw::serialPort::send( handle_t h, const void* byteA, unsigned byteN )
 }
 
 
-cw::rc_t cw::serialPort::receive( handle_t h, unsigned& readN_Ref)
+// Non-blocking read
+cw::rc_t cw::serialPort::receive_nb( handle_t h, unsigned userId, unsigned& readN_Ref, void* buf, unsigned bufN)
 {
-  rc_t         rc   = kOkRC;
-  port_t*        p    = _portHandleToPtr(h);
-  const unsigned bufN = 512;
-  char           buf[ bufN ];
+  rc_t      rc = kOkRC;
+  device_t* d  = _handleToPtr(h);
+  port_t*   p;
+
+  if((p = _idToPort(d,userId)) == nullptr )
+    return kInvalidArgRC;
+  
+  return _receive( d, p, readN_Ref, buf,bufN );
   
-  readN_Ref = 0;
-
-  if((rc = receive(h,buf,bufN,readN_Ref)) == kOkRC )
-    if( readN_Ref > 0 && p->_cbFunc != nullptr )
-      p->_cbFunc( p->_cbArg, buf, readN_Ref );
-
   return rc;
-  
 }
-  
+
 cw::rc_t cw::serialPort::receive( handle_t h, unsigned timeOutMs, unsigned& readN_Ref)
 {
-  rc_t rc;
-  port_t* p = _portHandleToPtr(h);
+  device_t* d = _handleToPtr(h);
 
-  if((rc = _poll(p,timeOutMs)) == kOkRC )
-    rc = receive(h,readN_Ref);
-  return rc;
+  return _poll(d,timeOutMs,readN_Ref);
   
 }
 
-cw::rc_t cw::serialPort::receive( handle_t h, void* buf, unsigned bufN, unsigned& readN_Ref)
+cw::rc_t cw::serialPort::receive( handle_t h, unsigned timeOutMs, unsigned& readN_Ref, unsigned userId, void* buf, unsigned bufByteN )
 {
- rc_t rc = kOkRC;
-  port_t* p = _portHandleToPtr(h);
+  device_t* d  = _handleToPtr(h);
+  port_t*   p;
   
-  readN_Ref = 0;
+  if((p = _idToPort(d,userId)) == nullptr )
+    return kInvalidArgRC;
   
-  if( !isopen(h)  )
-    return cwLogWarningRC( kResourceNotAvailableRC, "An attempt was made to read from a closed serial port.");
-  
-  int       n    = 0;
-  
-  // if attempt to read the port succeeded ...
-  if((n =read( p->_deviceH, buf, bufN )) != -1 )
-    readN_Ref = n;
-  else
-  {
-    // ... or failed and it wasn't because the port was empty
-    if( errno != EAGAIN)
-      rc = cwLogSysError(kReadFailRC,errno,"An attempt to read the serial port '%s' failed.", p->_deviceStr );
-  }
-    
-  return rc;
+  return _poll(d,timeOutMs,readN_Ref,userId,buf,bufByteN);
 }
-    
-cw::rc_t cw::serialPort::receive( handle_t h, void* buf, unsigned bufByteN, unsigned timeOutMs, unsigned& readN_Ref )
-{
-  rc_t rc = kOkRC;
-  port_t* p = _portHandleToPtr(h);
-  if((rc = _poll(p,timeOutMs)) == kOkRC )
-    rc = receive(h,buf,bufByteN,readN_Ref);
   
-  return rc;  
-}
-
-const char* cw::serialPort::device( handle_t h)
+  const char* cw::serialPort::device( handle_t h, unsigned userId)
 {
-  port_t* p = _portHandleToPtr(h);
+  device_t* d = _handleToPtr(h);
+  port_t*   p;
+  if((p = _idToPort(d,userId)) == NULL)
+    return NULL;
+  
   return p->_deviceStr;
 }
     
-unsigned    cw::serialPort::baudRate( handle_t h)
+unsigned    cw::serialPort::baudRate( handle_t h, unsigned userId )
 {
-  port_t* p = _portHandleToPtr(h);
+  device_t* d = _handleToPtr(h);
+  port_t*   p;
+  if((p = _idToPort(d,userId)) == NULL)
+    return 0;
+  
   return p->_baudRate;
 }
 
-unsigned    cw::serialPort::cfgFlags( handle_t h)
+unsigned    cw::serialPort::cfgFlags( handle_t h, unsigned userId )
 {
-  port_t* p = _portHandleToPtr(h);
+  device_t* d = _handleToPtr(h);
+  port_t*   p;
+  if((p = _idToPort(d,userId)) == NULL)
+    return 0;
+  
   return p->_cfgFlags;
 }
 
-unsigned cw::serialPort::readInBaudRate( handle_t h )
+unsigned cw::serialPort::readInBaudRate( handle_t h, unsigned userId  )
 {
 	struct termios attr;
-  port_t* p = _portHandleToPtr(h);
-	
+  device_t* d = _handleToPtr(h);
+  port_t*   p;
+  if((p = _idToPort(d,userId)) == NULL)
+    return 0;
+  
 	if((_getAttributes(p,attr)) != kOkRC )
 		return 0;
 
@@ -407,11 +627,14 @@ unsigned cw::serialPort::readInBaudRate( handle_t h )
   
 }
 
-unsigned cw::serialPort::readOutBaudRate( handle_t h)
+unsigned cw::serialPort::readOutBaudRate( handle_t h, unsigned userId )
 {
 	struct termios attr;
-  port_t* p = _portHandleToPtr(h);
-	
+  device_t* d = _handleToPtr(h);
+  port_t*   p;
+  if((p = _idToPort(d,userId)) == NULL)
+    return 0;
+  
 	if((_getAttributes(p,attr)) != kOkRC )
 		return 0;
 		
@@ -419,12 +642,16 @@ unsigned cw::serialPort::readOutBaudRate( handle_t h)
   
 }
 
-unsigned cw::serialPort::readCfgFlags( handle_t h)
+unsigned cw::serialPort::readCfgFlags( handle_t h, unsigned userId )
 {
 	struct termios attr;	
-	unsigned result = 0;
-  port_t* p = _portHandleToPtr(h);
-
+	unsigned       result = 0;
+  device_t*      d      = _handleToPtr(h);
+  port_t*        p;
+  
+  if((p = _idToPort(d,userId)) == NULL)
+    return 0;
+  
 	if((_getAttributes(p,attr)) == false )
 		return 0;
 
diff --git a/cwSerialPort.h b/cwSerialPort.h
index 13a98e8..0eed4bf 100644
--- a/cwSerialPort.h
+++ b/cwSerialPort.h
@@ -31,42 +31,49 @@ namespace cw
     };
 
 
-    typedef handle<struct port_str> handle_t;
-    typedef void (*callbackFunc_t)( void* cbArg, const void* byteA, unsigned byteN );
+    typedef handle<struct device_str> handle_t;
+    typedef void (*callbackFunc_t)( void* cbArg, unsigned userId, const void* byteA, unsigned byteN );
 
+    rc_t create(  handle_t& h, unsigned recvBufByteN=512 );
+    rc_t destroy( handle_t& h );
     
-    rc_t create( handle_t& h, const char* device, unsigned baudRate, unsigned cfgFlags, callbackFunc_t cbFunc, void* cbArg );
-    rc_t destroy(handle_t& h );
+    rc_t createPort(  handle_t h, unsigned userId, const char* device, unsigned baudRate, unsigned cfgFlags, callbackFunc_t cbFunc, void* cbArg );
+    rc_t destroyPort( handle_t h, unsigned userId );
 
-    bool isopen( handle_t h);
+    unsigned portCount( handle_t h );
+    unsigned portIndexToId( handle_t h, unsigned index );
+
+    bool isopen( handle_t h, unsigned userId );
     
-    rc_t send( handle_t h, const void* byteA, unsigned byteN );
+    rc_t send( handle_t h, unsigned userId, const void* byteA, unsigned byteN );
 
 
-    // Make callback to listener with result of read - Non-blocking
-    rc_t receive( handle_t h, unsigned& readN_Ref);
+    // Non-blocking - Receive data from a specific port if data is available.
+    // If buf==nullptr then use the ports callback function to deliver the received data,
+    // otherwise return the data in buf[bufByteN].
+    rc_t receive_nb( handle_t h, unsigned userId, unsigned& readN_Ref, void* buf=nullptr, unsigned bufByteN=0);
   
-    // Make callback to listener with result of read - Block for up to timeOutMs.
+    
+    // Blocking - Wait up to timeOutMs milliseconds for data to be available on any of the ports.
+    // Deliver received data via the port callback function.
+    // readN_Ref returns the total count of bytes read across all ports.
     rc_t receive( handle_t h, unsigned timeOutMs, unsigned& readN_Ref); 
 
-    // Return result of read in buf[bufByteN] - Non-blocking.
-    rc_t receive( handle_t h, void* buf, unsigned bufByteN, unsigned& readN_Ref);
-    
-    // Return result of read in buf[bufByteN] - Block for up to timeOutMs.
-    rc_t receive( handle_t h, void* buf, unsigned bufByteN, unsigned timeOutMs, unsigned& readN_Ref );
+    // Blocking - Wait up to timeOutMs milliseconds for data to be available on a specific port. Return the received data in buf[bufByteN].
+    rc_t receive( handle_t h, unsigned timeOutMs, unsigned& readN_Ref, unsigned userId, void* buf, unsigned bufByteN );
 
-    const char* device( handle_t h);
+    const char* device( handle_t h, unsigned userId );
     
     // Get the baud rate and cfgFlags used to initialize the port
-    unsigned    baudRate( handle_t h);
-    unsigned    cfgFlags( handle_t h);
+    unsigned    baudRate( handle_t h, unsigned userId );
+    unsigned    cfgFlags( handle_t h, unsigned userId );
 
     // Get the baud rate and cfg flags by reading the device.
     // Note the the returned buad rate is a system id rather than the actual baud rate,
     // however the cfgFlags are converted to the same kXXXFl defined in this class.
-    unsigned readInBaudRate( handle_t h );
-    unsigned readOutBaudRate( handle_t h);
-    unsigned readCfgFlags( handle_t h);
+    unsigned readInBaudRate(  handle_t h, unsigned userId );
+    unsigned readOutBaudRate( handle_t h, unsigned userId );
+    unsigned readCfgFlags(    handle_t h, unsigned userId );
   }
 }
 
diff --git a/cwSerialPortSrv.cpp b/cwSerialPortSrv.cpp
index a686e2b..bd73436 100644
--- a/cwSerialPortSrv.cpp
+++ b/cwSerialPortSrv.cpp
@@ -13,9 +13,9 @@ namespace cw
   {
     typedef struct this_str
     {
-      serialPort::handle_t portH;
+      serialPort::handle_t mgrH;
       thread::handle_t     threadH;
-      unsigned            _pollPeriodMs;
+      unsigned             pollPeriodMs;
     } this_t;
 
     inline this_t* _handleToPtr( handle_t h ) { return handleToPtr<handle_t,this_t>(h); }
@@ -23,25 +23,57 @@ namespace cw
     rc_t _destroy( this_t* p )
     {
       rc_t rc = kOkRC;
-      
-      if((rc = serialPort::destroy(p->portH)) != kOkRC )
-        return rc;
 
       if((rc = thread::destroy(p->threadH)) != kOkRC )
         return rc;
+      
+      if((rc = serialPort::destroy(p->mgrH)) != kOkRC )
+        return rc;
+
 
       mem::release(p);
 
       return rc;
     }
-    
+
+    // Do periodic non-blocking reads of each serial port and sleep between reads.
+    bool threadCallbackAlt( void* arg )
+    {
+      this_t*  p     = static_cast<this_t*>(arg);
+      unsigned portN = serialPort::portCount( p->mgrH );
+
+      unsigned readN;
+      
+      for(unsigned i=0; i<portN; ++i)
+      {
+        
+        rc_t rc = serialPort::receive_nb( p->mgrH, serialPort::portIndexToId(p->mgrH,i), readN );
+        
+        if( rc != kOkRC && rc != kTimeOutRC )
+        {
+          cwLogError(rc,"Serial server receive failed.");
+          return false;
+        }
+      }
+
+      if( readN == 0)
+        sleepMs(20);
+
+      return true;
+    }
+
+    // Wait for data to arrive on any port.
     bool threadCallback( void* arg )
     {
       this_t* p = static_cast<this_t*>(arg);
 
       unsigned readN;
-      if( serialPort::isopen(p->portH) )
-        serialPort::receive(p->portH,p->_pollPeriodMs,readN);
+      rc_t rc = serialPort::receive(p->mgrH,p->pollPeriodMs,readN);
+      if( rc != kOkRC && rc != kTimeOutRC )
+      {
+        cwLogError(rc,"Serial server receive failed.");
+        return false;
+      }
       
       
       return true;
@@ -51,19 +83,19 @@ namespace cw
 
 
 
-cw::rc_t cw::serialPortSrv::create( handle_t& h, const char* deviceStr, unsigned baudRate, unsigned cfgFlags, serialPort::callbackFunc_t cbFunc, void* cbArg, unsigned pollPeriodMs )
+cw::rc_t cw::serialPortSrv::create( handle_t& h, unsigned pollPeriodMs, unsigned recvBufByteN )
 {
   rc_t rc = kOkRC;
 
   this_t* p = mem::allocZ<this_t>();
-      
-  if((rc = serialPort::create( p->portH, deviceStr, baudRate, cfgFlags, cbFunc, cbArg )) != kOkRC )
-    goto errLabel;
+
+  if((rc = serialPort::create( p->mgrH, recvBufByteN)) != kOkRC )
+      goto errLabel;
 
   if((rc = thread::create( p->threadH, threadCallback, p)) != kOkRC )
     goto errLabel;
 
-  p->_pollPeriodMs = pollPeriodMs;
+  p->pollPeriodMs = pollPeriodMs;
 
  errLabel:
   if( rc != kOkRC )
@@ -91,10 +123,10 @@ cw::rc_t cw::serialPortSrv::destroy(handle_t& h )
 }
 
 
-cw::serialPort::handle_t cw::serialPortSrv::portHandle( handle_t h )
+cw::serialPort::handle_t cw::serialPortSrv::serialHandle( handle_t h )
 {
   this_t* p = _handleToPtr(h);
-  return p->portH;
+  return p->mgrH;
 }
 
 cw::thread::handle_t cw::serialPortSrv::threadHandle( handle_t h )
@@ -116,22 +148,22 @@ cw::rc_t cw::serialPortSrv::pause( handle_t h )
 }
 
 
-cw::rc_t cw::serialPortSrv::send( handle_t h, const void* byteA, unsigned byteN )
+cw::rc_t cw::serialPortSrv::send( handle_t h, unsigned portId, const void* byteA, unsigned byteN )
 {
   this_t* p = _handleToPtr(h);
-  return cw::serialPort::send(p->portH,byteA,byteN);
+  return cw::serialPort::send(p->mgrH,portId,byteA,byteN);
 }
 
 
 namespace cw
 {
 
-  void serialPortSrvTestCb( void* arg, const void* byteA, unsigned byteN )
+  void serialPortSrvTestCb( void* arg, unsigned userId, const void* byteA, unsigned byteN )
   {
     const char* text = static_cast<const char*>(byteA);
       
     for(unsigned i=0; i<byteN; ++i)
-      printf("%c:%i ",text[i],(int)text[i]);
+      printf("id:%i %c:%i\n",userId,text[i],(int)text[i]);
 
     if( byteN )
       fflush(stdout);      
@@ -140,19 +172,31 @@ namespace cw
 
 cw::rc_t cw::serialPortSrvTest()
 {
-  // Use this test an Arduino running study/serial/arduino_xmt_rcv/main.c  
-  rc_t                      rc             = kOkRC;
-  const char*               device         = "/dev/ttyACM0";
-  unsigned                  baud           = 38400;
-  unsigned                  serialCfgFlags = serialPort::kDefaultCfgFlags;
-  unsigned                  pollPeriodMs   = 50;
-  serialPortSrv::handle_t   h;
+  // Use this test an Arduino running study/serial/arduino_xmt_rcv/main.c
   
-  rc = serialPortSrv::create(h,device,baud,serialCfgFlags,&serialPortSrvTestCb,nullptr,pollPeriodMs);
+  rc_t                    rc               = kOkRC;
+  bool                    quitFl           = false;
+  unsigned                pollPeriodMs     = 50;
+  unsigned                portId[]         = {0,1};
+  const char*             device[]         = {"/dev/ttyACM1","/dev/ttyACM0"};
+  unsigned                baud[]           = {38400,38400};
+  unsigned                serialCfgFlags[] = {serialPort::kDefaultCfgFlags,serialPort::kDefaultCfgFlags};
+  unsigned                portN            = 2; //sizeof(portId)/sizeof(portId[0]);
+  unsigned                portIdx          = 0;  
+  serialPortSrv::handle_t h;
 
+  // open the serial port mgr
+  if((rc = serialPortSrv::create(h,pollPeriodMs)) != kOkRC )
+    return rc;
+
+  // open the serial ports
+  for(unsigned i=0; i<portN; ++i)
+    if((rc = serialPort::createPort( serialPortSrv::serialHandle(h), portId[i], device[i], baud[i], serialCfgFlags[i], &serialPortSrvTestCb, nullptr)) != kOkRC )
+      goto errLabel;
+
+  // start the server
   serialPortSrv::start(h);
   
-  bool quitFl = false;
   printf("q=quit\n");
   while(!quitFl)
   {
@@ -162,11 +206,17 @@ cw::rc_t cw::serialPortSrvTest()
       quitFl = true;
     else
       if( '0' <= c and c <= 'z' )
-        serialPortSrv::send(h,&c,1);
+      {
+        // send the output to consecutive ports
+        serialPortSrv::send(h,portId[portIdx],&c,1);
+        portIdx = (portIdx+1) % portN;
+      }
       
     
   }
 
+ errLabel:
+  
   serialPortSrv::destroy(h);
   return rc;
 }
diff --git a/cwSerialPortSrv.h b/cwSerialPortSrv.h
index ee972ec..4521ab0 100644
--- a/cwSerialPortSrv.h
+++ b/cwSerialPortSrv.h
@@ -7,16 +7,16 @@ namespace cw
   {
     typedef handle<struct this_str> handle_t;
 
-    rc_t create( handle_t& h, const char* device, unsigned baudRate, unsigned cfgFlags, serialPort::callbackFunc_t cbFunc, void* cbArg, unsigned pollPeriodMs );
+    rc_t create( handle_t& h, unsigned pollPeriodMs=50, unsigned recvBufByteN=512 );
     rc_t destroy(handle_t& h );
 
-    serialPort::handle_t  portHandle(   handle_t h );
+    serialPort::handle_t  serialHandle(   handle_t h );
     thread::handle_t      threadHandle( handle_t h );
 
     rc_t start( handle_t h );
     rc_t pause( handle_t h );
 
-    rc_t send( handle_t h, const void* byteA, unsigned byteN );
+    rc_t send( handle_t h, unsigned portId, const void* byteA, unsigned byteN );
   }