OS/2 Warp FAQ List (20 Feb 95) Section 0204

(2.4) COM3 and COM4 Support

Can I use COM3 and COM4 in OS/2 Warp?

COM3 and COM4 are supported on most PS/2s without any additional effort. On ISA, EISA, PCI, and VESA LocalBus machines, some additions are required to CONFIG.SYS. Using a text editor, include "(port number, base address, interrupt number)" parameters next to the COM.SYS filename. One example:

DEVICE=C:\OS2\BOOT\COM.SYS (3,3E8,5) (4,2E8,10)

Parameters for COM1 and COM2 need not be included (unless they are somehow nonstandard). OS/2 Warp must end up with sequentially numbered logical COM ports, if possible. For example, if (physical) port two is not installed but port three or port four is installed, start numbering using (2,...) in the DEVICE lines. See the OS/2 Warp printed manual and the online Command Reference for more information. If these efforts fail, try the SIO drivers [available from (3.2) Shareware and Freeware Sources]. Note that IRQ 2 is actually redirected to IRQ 9 on the AT bus, so use (...,...,9) in the above COM.SYS settings if your serial port is set to use IRQ 2.

AT bus COM ports cannot be used at the same time if they share interrupts because of bus design limitations (cf. "Under the Hood: How Interrupts Work," Byte, February, 1992). An adapter which provides more flexibility in interrupt selection [e.g. the 16-bit model from STB; see (2.5) Specific Hardware Recommendations] may prove helpful. Also, PolyCom, a replacement driver available from (3.2) Shareware and Freeware Sources, supports up to eight ports with the right hardware (Xenix-compatible multiport adapters).

"Smart" (coprocessor controlled) multiport communication adapters should be used when installing more than four ports. Such an adapter will work with OS/2 if the manufacturer has written an appropriate driver. Examples include:

Telephone Number
(800) PS2-2227
(612) 943-9020
(216) 349-1860
(615) 834-8000
(404) 475-2725
(612) 631-7654
CTC Systems
(415) 966-1688
(305) 255-3500
(214) 956-7770
(408) 378-7919
(408) 395-5775
(216) 434-3154

Related information:

(2.5) Specific Hardware Recommendations
(3.2) Shareware and Freeware Sources
(4.1) Installation

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