This article was previously published under Q99026
Computers running Microsoft Windows NT, Windows 2000, or Windows XP may be unable to set the same serial baud rates due to differences in serial port hardware on various platforms and computers. These differences may be important to note when writing a serial communications application that runs on different Windows NT, Windows 2000, or Windows XP platforms.
The simplest way to determine what baud rates are available on a particularserial port is to call the GetCommProperties() application programminginterface (API) and examine the COMMPROP.dwSettableBaud bitmask todetermine what baud rates are supported on that serial port.
Some baud rates may be available on one machine and not on another becauseof differences in the serial port hardware used on the two machines. MostIntel 80x86 machines use a standard 1.8432 megahertz (MHz) clock speed onserial port hardware, and therefore most Intel machines can set the samebaud rates. However, on other platforms, such as MIPS, there is no standardserial port clock speed. MIPS serial ports are known to exist with 1.8432MHz, 3.072 MHz, 4.2336 MHz, and 8.0 MHz serial port clock chips. Future NTimplementations on other platforms may have different serial port clockspeeds as well.
Furthermore, certain requested baud rates are special-cased in the WindowsNT serial driver so that they will work. The following are these specialcases: