DHU(4)                                                                  DHU(4)



NAME
       dhu - DHU-11 communications multiplexer

SYNOPSIS
       device dhu0 at uba0 csr 0160440 vector dhurint dhuxint

DESCRIPTION
       A DHU-11 provides 16 communication lines.

       Each  line attached to the DHU-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 13 speeds (50, 200 and 38400 baud are not
       available); see _t_t_y(4) for the encoding.

       Bit _i of flags may be specified for a DHU-11 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 dhu0 would cause line ttyS2 to be treated in this way.

       The DHU-11 driver normally uses input silos and delays receiver  inter‐
       rupts  by 20 milliseconds rather than taking an interrupt on each input
       character.

FILES
       /dev/tty[S-Z][0-9a-f]

SEE ALSO
       tty(4)

DIAGNOSTICS
       dhu(%d,%d): NXM fault.  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 RK07s) are present.  It is
       not serious.

       dhu%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 may then print a  mes‐
       sage on the console with interrupts disabled.

NOTES
       The  driver  currently does not make full use of the hardware capabili‐
       ties of the DHU-11, for dealing with  XON/XOFF  flow-control  or  hard-
       wired lines for example.

       Although  the devices are not the same, a DHU-11 can convince the DH-11
       autoconfiguration code that it is a DH-11.

       The 4 40-way cables are a pain.



4.3 Berkeley Distribution       April 27, 1986                          DHU(4)