This is a proposal for a C++ class to handle simple serial communications, which means send and receive some bytes, and control the state of serial communication signals. In many cases, what one needs is to be able to communicate by a serial port to certain devices or electronic circuits. As simplicity is the main goal in this class, it is developed for synchronous read and write operation instead of overlapped ones and also assuming that there is no hardware (or software) flow control so the communications signals can be freely controlled. If you need an event driven serial communication (overlapped read/write, signals changes controlled by even, etc.) you can look in this site for the article Serial communication for Win32 with modem support By thierrydollar
Using the code
To use the class
CSerialPort you must call
CSerialPort::Open then does read or write operation, set or test the state of communications signals and closes the port once finished (not mandatory because the destructor does it). The read and write methods make no assumption about type and format of data send or received, you must take into account if you are handling a character or binary format, if there is Unicode, mbcs, etc. The open function if defined as follows:
virtual BOOL Open(LPCTSTR PortName, DWORD BaudRate, BYTE ByteSize, <BR> BYTE Parity, BYTE StopBits,
DWORD DesiredAccess = GENERIC_READ|GENERIC_WRITE);
There is no assumption about communication parameters because they are specific to each serial communication and must be known in order to establish a successful communication. Even, if the most frequent name of serial ports are “COM1:” to “COM4:”, there can be more than 4 serial ports in a machine and the serial driver is not forced to follow the “COMxx” name convention so a serial port can have any name in Win32 platforms. It would be a good idea to have a static function to obtain the names of installed serial ports but, as far as I know, there is not a documented way to do that. There is a simple way to know about installed ports: assuming that ports names follow the “COMxx:” convention they try to open all possible ports and if there is an error and
ERROR_FILE_NOT_FOUND then the port isn’t installed. There is another way to know installed ports names and it is searching in registry but it is undocumented and platform depend.
With article there is a simple sample of using the mentioned class, the example is a program that reads bar codes from a serial bar code reader. Normally bar code readers send the read bar code ended by carriage return and line feed characters (this can be configured and even could be different for specific manufacturer) and the code is an ASCII string. There is a class (
CBarCodeReader ) derived from
CSerialPort that encapsulate the described protocol and its read method returns the read bar code (if any) directly in an string. There is not much more to say, the rest is in the code and it is simple (at least should be :-) )
Remember that this is a simple instead of complete way of using serial devices. The proposed code can be used in Win32 Platforms and Windows CE versions. Pocket PC developers (I didn’t try others Windows CE versions) must take into account that manufacturers can have specific implementations of serial APIs (as other APIs). Even if it is true that such implementations must agree to Pocket PC implementation, I have found small differences from one device to another. For instance: in a Dell Axim Pocket PC device the signal CD must be externally supplied (the voltage present) in order to read or do any operation with serial port, there is no function errors if you try without that signal on, but you won’t obtain any result. I have tried the same in Compaq iPAQs and it is possible to read without any specific external signal on (as should be).