[TOP] Error Reading From Serial Device Interfaces
Reading and Writing Serial Interfaces (APIs) that control Driver will not work to control the device.. If the standard serial communications driver will not Allen Denver Microsoft Windows Developer Support December 11, 1995 Summary: Learn about serial communications in Microsoft Windows.
This article assumes you are familiar with the fundamentals of multiple threading and synchronization in Windows.. • fdwCreate must specify the OPEN_EXISTING flag • hTemplateFile parameter must be NULL.
TAPI does deserve mention, however, in that it very nicely implements modem interfacing and call controlling.. The sample employs a few different data heaps for memory management It also makes extensive use of synchronization methods to facilitate communication between threads.
The sample included with this article, MTTTY: Multithreaded TTY (4918 exe), implements many of the features discussed here.. It uses three threads in its implementation: a user interface thread that does memory management, a writer thread that controls all writing, and a reader/status thread that reads data and handles status changes on the port.. In other words, get your feet wet before diving in head first (36 printed pages) Introduction This article does not discuss TAPI.. This will allow seamless integration with the other TAPI-enabled applications that a user may have.. The following is the proper way to open a communications resource for overlapped operation.. Some systems even have more ports than the traditional maximum of four Hardware vendors and serial-device-driver writers are free to name the ports anything they like.. For applications not using TAPI, handle inheritance or duplication is necessary to share the communications port.. Readers unfamiliar with general Windows programming practices should learn some of the fundamentals of general Windows programming before taking on serial communications.. Opening a Port The CreateFile function opens a communications port There are two ways to call CreateFile to open the communications port: overlapped and nonoverlapped.. Communications ports cannot be shared in the same manner that files are shared Applications using TAPI can use the TAPI functions to facilitate sharing resources between applications.. One thing to note about port names is that traditionally they have been COM1, COM2, COM3, or COM4.. HANDLE hComm; hComm = CreateFile( gszPort, GENERIC_READ| GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, 0); if (hComm == INVALID_HANDLE_VALUE) // error opening port; abort Removal of the FILE_FLAG_OVERLAPPED flag from the call to CreateFile specifies nonoverlapped operation.. Application programming interfaces (APIs) that control user interface features of windows and dialog boxes, though not discussed here, are useful to know in order to fully comprehend the sample provided with this article.. The next section discusses overlapped and nonoverlapped operations The Platform SDK documentation states that when opening a communications port, the call to CreateFile has the following requirements: • fdwShareMode must be zero.. When an event relating to an IN endpoint (data transmitted from the device to the host) is received, the status read from USBEndpointStatus() indicates any errors in transmission.. A production application that works with modems and makes telephone calls should implement these features using the TAPI interface.. For this reason, it is best that users have the ability to specify the port name they want to use.. The actual number used with the MI_∗ value is the interface number assigned to the serial device.. Handle duplication is beyond the scope of this article; please refer to the Platform SDK documentation for more information.. Contents Overview This article provides a foundation for learning about serial communications in Windows.. Furthermore, this article does not discuss some of the configuration functions, such as GetCommProperties.. The Windows API does not provide any mechanism for determining what ports exist on a system.. If a port does not exist, an error will occur (ERROR_FILE_NOT_FOUND) after attempting to open the port, and the user should be notified that the port isn't available.. In addition, a basic familiarity of the heap functions is useful to fully comprehend the memory management methods used by the sample, MTTTY, included with this article.
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