2.9BSD/usr/man/man4/dh.4

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.TH DH 4
.UC
.SH NAME
dh/dm \- DH-11/DM-11 communications multiplexer
.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
.IR tty (4).
Input and output for each line may independently
be set to run at any of 16 speeds;
see
.IR tty (4)
for the encoding.
.PP
DH lines for which the corresponding minor device numbers
have the 0200 bit set are treated as having no modem control.
.SH FILES
.ta 2i
/dev/tty[hi][0-9a-f]
.br
/dev/ttyd[0-9a-f]	dialups
.SH "SEE ALSO"
tty(4)
.SH DIAGNOSTICS
\fBdh%d: silo overflow\fP.  The 64 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
.IR net (1)
is running on a
.I dh
line at high speed (e.g. 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.