4.3BSD-UWisc/man/cat4/dh.4

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



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

SYNOPSIS
     device dh0 at uba0 csr 0160020 vector dhrint dhxint
     device dm0 at uba0 csr 0170500 vector dmintr

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.

     Bit _i of flags may be specified for a 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.

     The _d_h driver monitors the rate of input on each board, and
     switches between the use of character-at-a-time interrupts
     and input silos.  While the silo is enabled during periods
     of high-speed input, the driver polls for input 30 times per
     second.

FILES
     /dev/tty[h-o][0-9a-f]
     /dev/ttyd[0-9a-f]

SEE ALSO
     tty(4)

DIAGNOSTICS
     dh%d: NXM.  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.

     dh%d: silo overflow.  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.  It is not serious.







Printed 12/27/86          May 16, 1986                          1