Important Notice

The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

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The Windows 3.1 communications driver (COMM.DRV) accesses serial ports COM1,
COM2, COM3, and COM4 using base-address values specified in the BIOS data
area of a computer. If the BIOS data area does not specify values for
physical ports, Windows 3.1 will use the base address, 0x03E8, and IRQ4 for
COM3, but the base addresses and IRQs for the other ports must be set by the
user.
 
If the BIOS data area does not specify a value for a physical port, the user
can set the base address and IRQ values using Control Panel. Control Panel
displays an Advanced settings dialog box for each port. The dialog box
contains a selection box for base addresses and spin controls for IRQ
settings. The selected values are recorded as COMxBase and COMxIRQ settings
in the [386Enh] section of the SYSTEM.INI file.
 
The COMxBase and COMxIRQ settings are used for both standard- and 386
enhanced-mode operation. The COMxBase setting is used only if the BIOS data
area does not specify a value for the port; this setting never overrides the
BIOS data area values.
 
 
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