Microsoft KB Archive/82641

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Windows 3.1 Serial Communications Improvements

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Q82641

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The information in this article applies to:


 * Microsoft Windows versions 3.1, 3.11

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SUMMARY
All Windows communications applications will benefit from the improved system-wide communications features in Microsoft Windows operating system version 3.1. Most of the serial communications problems experienced by users of Windows 3.0 are corrected in Windows 3.1. Below is a summary of the changes:


 * COM port addresses and IRQs can be configured in the Control Panel. Windows 3.0 used preset address values for serial ports. Windows 3.1 now allows any port address and IRQ to be used. This solves problems using ports COM3 and COM4, for which Windows 3.0 used nonstandard default values.
 * Faster bit rates. Applications for Windows can now set speeds higher than 19.2 kilobits per second (Kbps), up to 57.6 Kbps. Contact your Windows software manufacturer for an update to support this new feature.
 * Reduced system overhead. Windows 3.1 is fine-tuned for better performance overall, including faster throughput and fewer errors during serial communications. A new driver interface allows Windows to pass data in blocks to the driver, rather than passing data a character at a time. See the Windows 3.1 Device Development Kit (DDK) for details. Windows 3.0 passes data one character at a time.
 * The high-speed 16550 UART (Universal Asynchronous Receiver Transmitter) is now supported for Windows applications.
 * EnableCommNotification API. Windows applications can register to be notified by a window message when serial port events occur, rather than performing constant polling, which reduces overall system performance.
 * Serial ports on the same IRQ can be used &quot;in rotation.&quot; Although on most PCs, serial ports that use the same IRQ cannot be used simultaneously, Windows 3.0 sometimes prevented them from being used in rotation, one after another. This is corrected in Windows 3.1.
 * Full-duplex improvements. Some users experienced lockups during full-duplex transfers at fast bit rates under Windows 3.0. These problems are corrected in Windows 3.1.

KBCategory: kbusage

KBSubcategory: win31 wincomm

Additional query words: 3.10 3.11 3.1

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Technology : kbWin3xSearch kbWin310 kbWin311