.\"	$OpenBSD: com.4,v 1.1 1998/09/24 04:43:05 rahnds Exp $
.\"	$NetBSD: com.4,v 1.5 1996/03/16 00:07:08 thorpej Exp $
.\"
.\" Copyright (c) 1990, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Systems Programming Group of the University of Utah Computer
.\" Science Department.
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     from: @(#)dca.4	5.2 (Berkeley) 3/27/91
.\"
.Dd July 12, 1998
.Dt COM 4 i386
.Os
.Sh NAME
.Nm com
.Nd
serial communications interface
.Sh SYNOPSIS
.Cd "com0 at isa? port" \&"IO_COM1\&" irq 4
.Cd "com1 at isa? port" \&"IO_COM2\&" irq 3
.Cd "com2 at isa? port" \&"IO_COM3\&" irq 1
.Cd "com3 at isa? port" \&"IO_COM4\&" irq 5
.Pp
.Sh DESCRIPTION
The
.Nm com
drivers provide support for NS8250-, NS16450-, NS16550- and ST16650-based
.Tn EIA
.Tn RS-232C
.Pf ( Tn CCITT
.Tn V.28 )
communications interfaces.
.Pp
The NS8250 and NS16450 have single
character buffers, the NS16550 has a 16 character buffer, while
the ST16650 has a 32 character buffer.  The XR16850 has a 128 character
buffer.
.Pp
Input and output for each line may set to one of following baud rates;
50, 75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, 9600,
19200, 38400, 57600, or 115200, or any other baud rate which is a factor
of 115200.
.Sh FILES
.Bl -tag -width Pa
.It Pa /dev/tty00
.It Pa /dev/tty01
.It Pa /dev/tty02
.It Pa /dev/tty03
.It Pa /dev/cua00
.It Pa /dev/cua01
.It Pa /dev/cua02
.It Pa /dev/cua03
.El
.Sh DIAGNOSTICS
.Bl -diag
.It com%d: %d silo overflows
The input
.Dq silo
has overflowed and incoming data has been lost.
.It com%d: weird interrupt: iir=%x
The device has generated an unexpected interrupt
with the code listed.
.El
.Sh SEE ALSO
.Xr ast 4 ,
.Xr rtfps 4 ,
.Xr tty 4
.Sh HISTORY
The
.Nm
driver was originally derived from the
.Nm HP9000/300
.Nm dca
driver and is
.Ud
.Sh BUGS
Data loss is possible on busy systems with unbuffered UARTs at high speed.
.Pp
The name of this driver and the constants which define the locations
of the various serial ports are holdovers from
.Nm DOS .