If you’re like me, you have
probably adopted the .NET framework as the basis for your latest Microsoft (MS)
development efforts in an attempt to keep current on the platform. In my
opinion, MS has done a very good job with the new framework and I especially
like the new C# language, which is what this project is programmed in.
Once you’ve learned your way
around the assemblies, it quickly becomes apparent that MS, in their infinite
wisdom, have totally ignored legacy serial ports and thus have not included any
way to efficiently access and manage the ports in their native assemblies. This
should come as no surprise – MS has always made it a pain to deal with serial
Since there was no way to efficiently and completely
manage serial ports provided in the assemblies, I had to rely on the old Win32
library calls for the necessary interfaces. To make these function calls
compatible with C# and OO methodology in general, they have all been packaged
in wrapper classes whose access is limited to the container class.
project contains a complete set of tools for the configuration and management
of legacy COM ports. The Settings form provides a tool for setting up the COM
port and saving the setup parameters to a user defined configuration file. The
Terminal form provides a model for how the base class can be instantiated and
how the delegates are defined and used to get access to the base overrides. The
terminal is a very useful tool for implementing and testing the serial classes
as well as testing any general serial communications.
Win32 Wrapper Classes
The Win32xxx files are internal
wrapper classes that are used only by the
SerialComm abstract class. This is done
to provide complete encapsulation of the Win32 functions. As you will see, each
of the Win32 function calls is private to the class and is
contained within a wrapper method. It is this wrapper method that is called by
SerialComm class. This approach provides controlled access to the legacy
functions. A brief summary of each class is as follows –
Win32Com – Contains the most basic com port interface functions – i.e.
CreateFile() (open the port)
CloseHandle() (close the
ReadFile() (read from port),
WriteFile() (write to
CancelIo() (cancel all pending I/O),
(purge I/O buffers) and
(special char transmit).
Win32DCB – Contains the
SetCommState() functions that control access to the Device Control Block
(DCB) and the properties that represent each member of the DCB control
structure that is used to control serial port behavior.
Win32Enums – Contains a set of public enumerations that are used by all
of the Win32 wrapper classes.
Win32Escape – Contains the
EscapeCommFunction() function, which directs a specified communications device
to perform an extended function.
Win32Events – Contains the
functions which control event setup and handling by the receiver.
Win32Modem – Contains the
GetCommModemStatus() function which returns the current states of the modem
control register. This register indicates the current state of the CTS, DSR,
RLSD and RING signals.
Win32Overlap – Contains the
GetOverlappedResult() function and the Overlapped structure
which provide a means to process serial I/O asynchronously.
Win32Properties – Contains the
GetCommProperties() functions which provide methods for reading and writing
certain port management properties – particularly the read/write queue sizes.
Win32Status – Contains the
function and port status structures.
Win32Timeouts – Contains the
SetCommTimeouts() functions and the Timeouts structure which control read/write
SerialComm Abstract Class
SerialComm is an abstract class that must be inherited to
get access to all of the public properties and methods that provide control
over the serial port(s). It instantiates all of the Win32xxx wrapper classes
and thus encapsulates them within the abstraction. This class exposes the
methods and properties needed by the inheriting class to control the port.
SerialComm also contains a number of protected
virtual event handlers – i.e. the
OnBreak, etc. methods. By overriding
these methods (as is done by the
SerialBase class), the inheriting class can
hook these functions to provide case specific functionality.
SerialComm also provides the receive thread that is
automatically started when the port is opened and stopped when the port is
closed. The receive thread handles any incoming data asynchronously from the
transmitter. Overlapping is used to more efficiently handle asynchronous I/O.
SerialConfig is the basic port
configuration class. It contains most of the members of the DCB as well as some
other properties that control timeouts, queue sizes and other parameters.
The Settings form usually handles
actual manipulation of the contents of this class. This tool provides the user
with a graphical means to configure the port. Not all members of the
configuration class appear on the form. In my implementation, those members
that are generally managed by the OS are not included. The user can easily add
these members to the form if so desired.
SerialBase is the base interface
class that inherits the
SerialComm class, instantiates a
SerialConfig class and
provides a delegate structure that permits the user to get access to the
protected virtual event handler methods from
is normally declared for each serial port that the user wishes to control.
SerialBase can either be inherited or instantiated, as is done by the Terminal
The Serial Test & Debug Terminal
The serial terminal application
TerminalMain class that contains the
Main() method for starting the
terminal. This means of starting the terminal is only used in this test
implementation – application startup would normally be done elsewhere.
The terminal constructor
demonstrates a typical implementation of how the serial base class is
instantiated and how the delegate classes are utilized. On or about Lines 125
& 129, the source declares a
SerialPort class and
which are initialized at the end of the constructor.
The end of the terminal file
contains the delegate methods that point to the overrides from the base class.
There is one for every virtual method currently declared, though not all may be
necessary in all implementations.
As I am sure that most of you can
appreciate, I have gone to a considerable amount of effort to put this project
together and am giving it away free of charge to all interested parties in the
hope that I will receive some constructive feedback. Since I do not, by any
means, consider myself an expert on the new .NET framework (nor C# for that
matter), I would greatly appreciate any comments on how useful you think this
software is to you, suggestions for improvements to the overall architecture
and/or the efficiency of the base classes, any bug reports, etc.
To reach me, please send all
comments to: email@example.com.
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Timothy J. Krell is a design engineer with over 25 years of experience in the areas of robotics, communications, automated systems design, mobile unmanned systems, GIS and software engineering.