.\"	$OpenBSD: com.4,v 1.4 2001/10/05 14:45:53 mpech 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
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.\" 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.
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\"
.\"     from: @(#)dca.4	5.2 (Berkeley) 3/27/91
.\"
.Dd August 6, 1993
.Dt COM 4 alpha
.Os
.Sh NAME
.Nm com
.Nd AlphaStation serial communications interface
.Sh SYNOPSIS
.Cd "com0 at isa? port" \&"IO_COM1\&" irq 4
.Cd "com1 at isa? port" \&"IO_COM2\&" irq 3
.Sh DESCRIPTION
The
.Nm
driver provides support for NS8250-, NS16450-, NS16550- and ST16650-based
.Tn EIA
.Tn RS-232C
.Pf ( Tn CCITT
.Tn V.28 )
communications interfaces.
The NS8250 and NS16450 have single character buffers, the NS16550 has a 16
character buffer, while the ST16650 has a 32 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/ttyC0
.It Pa /dev/ttyC1
.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 .