DH(4)               UNIX Programmer's Manual                DH(4)

NAME
     dh/dm - DH-11/DM-11 communications multiplexer

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.

     Each line attached to the DH-11 communications multiplexer
     behaves as described in _t_t_y(4).  Input and output for each
     line may independently be set to run at any of 16 speeds;
     see _t_t_y(4) for the encoding.

     DH lines for which the corresponding minor device numbers
     have the 0200 bit set are treated as having no modem con-
     trol.

FILES
     /dev/tty[hi][0-9a-f]
     /dev/ttyd[0-9a-f]   dialups

SEE ALSO
     tty(4)

DIAGNOSTICS
     dh%d: silo overflow.  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 _n_e_t(1) is running on a
     _d_h 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 cor-
     rupted, but the network will recover.  It is not serious.

Printed 5/18/83                                                 1