Microsoft KB Archive/60202

Use of COM3 and COM4 Ports Requires ROM BIOS Support PSS ID Number: Q60202 Article last modified on 02-02-1993 PSS database name: O_MSDOS

4.00

MS-DOS

Summary:

On Page 99 of the “Microsoft MS-DOS Version User’s Reference” Version 4.0 manual, the MODE command is described as being able to support ports COM3 and COM4. This description assumes that there is appropriate support in your computer’s ROM BIOS for ports COM3 and COM4. This assumption should be incorporated wherever ports COM3 and COM4 are mentioned, such as in the PRINT section.

If you want to use ports COM3 and COM4, the machine’s ROM BIOS has to be upgraded to support those ports. Conversely, most cards that provide COM3 and COM4 ports generally come with device drivers that are loaded in CONFIG.SYS. These device drivers should be used instead of the MODE command.

Additional reference words: 4.00 noupd

Copyright Microsoft Corporation 1993.