DOCUMENT:Q82641  02-OCT-1999  [win95x]
TITLE   :Windows 3.1 Serial Communications Improvements
PRODUCT :Microsoft Windows 95.x Retail Product
PROD/VER:WINDOWS:3.1,3.11
OPER/SYS:
KEYWORDS:

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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 "in rotation." 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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Keywords          :  
Technology        : kbWin3xSearch kbZNotKeyword3 kbWin310 kbWin311
Version           : WINDOWS:3.1,3.11

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