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    <p>You might try some code something like this after you've opened the file, but before you try to use it:</p> <pre><code>COMMTIMEOUTS timeouts; timeouts.ReadIntervalTimeout = 1; timeouts.ReadTotalTimeoutMultiplier = 1; timeouts.ReadTotalTimeoutConstant = 1; timeouts.WriteTotalTimeoutMultiplier = 1; timeouts.WriteTotalTimeoutConstant = 1; if (!SetCommTimeouts(m_hCommPort, &amp;timeouts)) // setting timeouts failed. </code></pre> <p>Edit: perhaps it's easier to start with some code that works, and make it do what you want rather than trying to get your code to work. Here's a simple terminal program. It's minimalist in the extreme, but does work (at least well enough to let me see output from my GPS, for one example). It's a long ways from what anybody (least of all me) would call sophisticated, but should give at least some idea of how to get started.</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;conio.h&gt; #include &lt;string.h&gt; #define STRICT #define WIN32_LEAN_AND_MEAN #include &lt;windows.h&gt; void system_error(char *name) { // Retrieve, format, and print out a message from the last error. The // `name' that's passed should be in the form of a present tense noun // (phrase) such as "opening file". // char *ptr = NULL; FormatMessage( FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM, 0, GetLastError(), 0, (char *)&amp;ptr, 1024, NULL); fprintf(stderr, "\nError %s: %s\n", name, ptr); LocalFree(ptr); } int main(int argc, char **argv) { int ch; char buffer[1]; HANDLE file; COMMTIMEOUTS timeouts; DWORD read, written; DCB port; HANDLE keyboard = GetStdHandle(STD_INPUT_HANDLE); HANDLE screen = GetStdHandle(STD_OUTPUT_HANDLE); DWORD mode; char port_name[128] = "\\\\.\\COM3"; char init[] = ""; // e.g., "ATZ" to completely reset a modem. if ( argc &gt; 2 ) sprintf(port_name, "\\\\.\\COM%c", argv[1][0]); // open the comm port. file = CreateFile(port_name, GENERIC_READ | GENERIC_WRITE, 0, NULL, OPEN_EXISTING, 0, NULL); if ( INVALID_HANDLE_VALUE == file) { system_error("opening file"); return 1; } // get the current DCB, and adjust a few bits to our liking. memset(&amp;port, 0, sizeof(port)); port.DCBlength = sizeof(port); if ( !GetCommState(file, &amp;port)) system_error("getting comm state"); if (!BuildCommDCB("baud=19200 parity=n data=8 stop=1", &amp;port)) system_error("building comm DCB"); if (!SetCommState(file, &amp;port)) system_error("adjusting port settings"); // set short timeouts on the comm port. timeouts.ReadIntervalTimeout = 1; timeouts.ReadTotalTimeoutMultiplier = 1; timeouts.ReadTotalTimeoutConstant = 1; timeouts.WriteTotalTimeoutMultiplier = 1; timeouts.WriteTotalTimeoutConstant = 1; if (!SetCommTimeouts(file, &amp;timeouts)) system_error("setting port time-outs."); // set keyboard to raw reading. if (!GetConsoleMode(keyboard, &amp;mode)) system_error("getting keyboard mode"); mode &amp;= ~ ENABLE_PROCESSED_INPUT; if (!SetConsoleMode(keyboard, mode)) system_error("setting keyboard mode"); if (!EscapeCommFunction(file, CLRDTR)) system_error("clearing DTR"); Sleep(200); if (!EscapeCommFunction(file, SETDTR)) system_error("setting DTR"); if ( !WriteFile(file, init, sizeof(init), &amp;written, NULL)) system_error("writing data to port"); if (written != sizeof(init)) system_error("not all data written to port"); // basic terminal loop: do { // check for data on port and display it on screen. ReadFile(file, buffer, sizeof(buffer), &amp;read, NULL); if ( read ) WriteFile(screen, buffer, read, &amp;written, NULL); // check for keypress, and write any out the port. if ( kbhit() ) { ch = getch(); WriteFile(file, &amp;ch, 1, &amp;written, NULL); } // until user hits ctrl-backspace. } while ( ch != 127); // close up and go home. CloseHandle(keyboard); CloseHandle(file); return 0; } </code></pre>
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    1. COok, this seems to fix the thread issue but I cannot seem to get the ReadFile() to populate my output array.
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    2. CO@lYriCAlsSH: see edited answer.
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    3. COI should clarify, I am attempting to communicate with an embedded system through serial and its request/response protocol is based on strings. I have it working on hyperTerminal but I am attempting to create my own code that does essentially the same thing.
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