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copied!<p><em>RTS_CONTROL_TOGGLE</em> does not work (has a variable 1-15 millisecond delay before turning it off after transmit) on our embedded XP platform. It's possible I could get that down if I altered the time quantum to 1 ms using timeBeginPeriod(1), etc, but I doubt it would be reliable or enough to matter. (The device responds @ 1 millisecond sometimes)</p> <p>The final solution is really ugly but it works on this hardware. I would not use it on anything where the hardware is not fixed in stone.</p> <p>Basically:</p> <p>1) set the FIFOs on the serial port's device manager page to off or 1 character deep</p> <p>2) send your message + <strong>2 extra bytes</strong> using this code:</p> <pre><code>int WriteFile485(HANDLE hPort, void* pvBuffer, DWORD iLength, DWORD* pdwWritten, LPOVERLAPPED lpOverlapped) { int iOldClass = GetPriorityClass(GetCurrentProcess()); int iOldPriority = GetThreadPriority(GetCurrentThread()); SetPriorityClass(GetCurrentProcess(), REALTIME_PRIORITY_CLASS); SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_TIME_CRITICAL); EscapeCommFunction(hPort, SETRTS); BOOL bRet = WriteFile(hPort, pvBuffer, iLength, pdwWritten, lpOverlapped); EscapeCommFunction(hPort, CLRRTS); SetPriorityClass(GetCurrentProcess(), iOldClass); SetThreadPriority(GetCurrentThread(), iOldPriority); return bRet; } </code></pre> <p>The WriteFile() returns when the last byte or two have been written to the serial port. They have NOT gone out the port yet, thus the need to send 2 extra bytes. One or both of them will get trashed when you do CLRRTS.</p> <p>Like I said... it's ugly.</p>

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