date and time created 85/07/25 12:10:50 by mckusick

SCCS-vsn: share/man/man4/man4.vax/dhu.4 6.1

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+.\" Copyright (c) 1985 Regents of the University of California.
+.\" All rights reserved.  The Berkeley software License Agreement
+.\" specifies the terms and conditions for redistribution.
+.\"
+.\"    @(#)dhu.4       6.1 (Berkeley) %G%
+.\"
+.TH DHU 4 ""
+.UC 6
+.SH NAME
+dhu \- DHU-11 communications multiplexer
+.SH SYNOPSIS
+.B "device dhu0 at uba0 csr 0160440 vector dhurint dhuxint"
+.SH DESCRIPTION
+A DHU-11 provides 16 communication lines.
+.PP
+Each line attached to the DHU-11 communications multiplexer
+behaves as described in
+.IR tty (4).
+Input and output for each line may independently
+be set to run at any of 13 speeds (50, 200 and 38400 baud are not available);
+see
+.IR tty (4)
+for the encoding.
+.PP
+Bit
+.I i
+of flags may be specified for a DHU-11 to say that a line is not properly
+connected, and that the line should be treated as hard-wired with carrier
+always present.  Thus specifying ``flags 0x0004'' in the specification of dhu0
+would cause line ttyh2 to be treated in this way.
+.PP
+The 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
+/dev/tty[hi][0-9a-f]
+.SH "SEE ALSO"
+tty(4)
+.SH DIAGNOSTICS
+\fBdhu(%d,%d): NXM fault\fR.  No response from UNIBUS on a dma transfer
+within a timeout period.  This is often followed by a UNIBUS adapter
+error.  This occurs most frequently when the UNIBUS is heavily loaded
+and when devices which hog the bus (such as rk07's) are present.
+It is not serious.
+.PP
+\fBdhu%d: silo overflow\fR.  The character input silo overflowed
+before it could be serviced.  This can happen if a hard error occurs
+when the CPU is running with elevated priority, as the system may
+then print a message on the console with interrupts disabled.
+.SH NOTES
+The driver currently does not make full use of the hardware
+capabilities of the DHU-11, for dealing with XON/XOFF flow-control or hard-wired
+lines for example.
+.PP
+Although the devices are not the same, a DHU-11 can convince the
+DH-11 autoconfiguration code that it is a DH-11.
+.PP
+The 4 40-way cables are a pain.