---
name: "addcom"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["openbsd"]
url: "https://new.carta.tech/addcom"
---

# addcom(4)

multiplexing serial communications interface

## NAME

**addcom** – multiplexing serial communications interface

## SYNOPSIS

**addcom0 at isa? port 0x108 irq 5** **com\* at addcom?**

## DESCRIPTION

The **addcom** driver provides support for Addonics FlexPort 8/S (and probably FlexPort 4/S) boards that multiplex together up to eight (or four) EIA RS-232C (CCITT V.28) communications interfaces.

Each **addcom** device is the master device for up to eight **com** devices. The kernel configuration specifies these **com** devices as slave devices of the **addcom** device, as shown in SYNOPSIS. The slave ID given for each **com** device determines which bit in the interrupt multiplexing register is tested to find interrupts for that device. The port specification for the **addcom** device is used to compute the base addresses for the **com** subdevices. The port for the interrupt multiplexing register is fixed, so it is doubtful that more than one **addcom** can be used in a machine.

## FILES

- */dev/tty??*

  ## SEE ALSO

[com(4)](/com/4.md), [intro(4)](/intro/4.md), [isa(4)](/isa/4.md)

## HISTORY

OpenBSD support for **addcom** devices first appeared in OpenBSD 3.0.