.\"	$OpenBSD: dhu.4,v 1.11 2003/06/06 10:29:42 jmc Exp $
.\"	$NetBSD: dhu.4,v 1.4 1996/03/05 15:28:48 ragge Exp $
.\"
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.\"     from: @(#)dhu.4	6.3 (Berkeley) 3/27/91
.\"
.Dd March 27, 1991
.Dt DHU 4 vax
.Os
.Sh NAME
.Nm dhu
.Nd
.Tn DHU-11/DHV-11
communications multiplexer
.Sh SYNOPSIS
.Cd "dhu0 at uba0 csr 0160440"
.Sh DESCRIPTION
A
.Tn DHU-11
provides 16 communication lines.
.Pp
Normal I/O
control parameters for individual lines are managed by
.Xr ioctl 2
calls.
Individual
.Tn DHU-11
lines may be configured to run at any of 13 speeds
(50, 200 and 38400 baud are not available);
the speed may be set via
.Xr getty 8
or
.Xr stty 1
or may be communicated by other programs which
utilize
.Xr ioctl 2
such as
.Xr ifconfig 8 ,
see
.Xr tty 4 .
.Pp
The
.Tn DHU-11
driver normally uses input silos
and delays receiver interrupts by 20 milliseconds
rather than taking an interrupt on each input character.
.Sh FILES
.Bl -tag -width /dev/tty[S-Z][0-9a-f]xx -compact
.It Pa /dev/tty[S-Z][0-9a-f]
.El
.Sh NOTES
The driver currently does not make full use of the hardware
capabilities of the
.Tn DHU-11 ,
for dealing with
.Tn XON/XOFF
flow-control or hard-wired
lines for example.
.Pp
Although the devices are not the same, a
.Tn DHU-11
can convince the
.Tn DH-11
autoconfiguration code that it is a
.Tn DH-11 .
.Pp
The 4 40-way cables are a pain.
.Sh SEE ALSO
.Xr tty 4 ,
.Xr uba 4
.Sh HISTORY
The
.Nm
driver appeared in
.Bx 4.3 .
A new
.Nm
driver showed up in
.Nx 1.1a .
.Sh BUGS
Even if the
.Nm
hardware supports
.Tn DMA ,
the driver cannot make use of this capability.