dh.4

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)dh.4	8.1	9/11/90
.TH dh 4 VAX "" Unsupported
.SH Name
dh \- DH-11/DM-11 communications multiplexer
.SH Syntax
.B "device dh0 at uba? csr 0160020 flags 0x???? vector dhrint dhxint"
.br
.B "device dm0 at uba? csr 0170500 flags 0x???? vector dmintr"
.SH Description
A DH-11 provides 16 communication lines; DM-11's may be optionally
paired with DH-11's to provide modem control for the lines.
.PP
Each line attached to the DH-11 communications multiplexer
behaves as described in
.MS tty 4 .
Input and output for each line may independently
be set to run at any of 16 speeds;
see
.MS tty 4
for the encoding.
.PP
Bit
.I i
of flags may be specified for a 
.PN dh 
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 dh0
would cause line ttyh2 to be treated in this way.
.PP
The 
.PN dh 
driver normally uses input silos
and polls for input at each clock tick (10 milliseconds)
rather than taking an interrupt on each input character.
.SH Diagnostics
.B "\fBdh%d: NXM\fR"
.br
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
.B "\fBdh%d: silo overflow\fR"
.br
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 will
then print a message on the console with interrupts disabled.  If the
Berknet
is running on a
.PN dh
line at high speed (for example, 9600 baud), 
there is only 1/15th of a second of
buffering capacity in the silo, and overrun is possible.  This may
cause a few input characters to be lost to users and a network
packet is likely to be corrupted, but the network will recover.
It is not serious.
.SH Files
.PN /dev/tty[h-o][0-9a-f]
.br
.PN /dev/ttyd[0-9a-f]
.SH See Also
tty(4)