4.3BSD - /usr/man/cat4/dh.0

DH(4)                                                                    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 tty(4).  Input and output for each line may independently
       be set to run at any of 16 speeds; see tty(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 dh 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 mes‐
       sage on the console with interrupts disabled.  It is not serious.


4th Berkeley Distribution        May 16, 1986                            DH(4)