1DHU(4)                     Kernel Interfaces Manual                     DHU(4)
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NAME

6       dhu - DHU-11 communications multiplexer
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SYNOPSIS

9       /sys/conf/SYSTEM:
10            NDHU dhu_units # DHU11
11
12       /etc/dtab:
13            #Name Unit# Addr   Vector Br Handler(s)      # Comments
14            du    ?     160020 310    5  dhurint dhuxint # dhu11 terminal mux
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16       major device number(s):
17            raw: 4
18       minor device encoding:
19            bits 0017 specify line on DHU unit
20            bits 0060 specify DHU unit
21            bit  0100 specify RTS/CTS flow control
22            bit  0200 specifies non-blocking open (``CD always on'')
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DESCRIPTION

25       A DHU-11 provides 16 communication lines.
26
27       Each  line attached to the DHU-11 communications multiplexer behaves as
28       described in tty(4).  Input and output for each line may  independently
29       be  set  to  run  at  any  of 13 speeds (50, 200 and 38400 baud are not
30       available); see tty(4) for the encoding.
31
32       Bit 0200 of the minor device number for DHU lines may  be  set  to  say
33       that  a  line  is  not  properly connected, and that the line should be
34       treated as hard-wired with carrier always present.  Thus  creating  the
35       special  character  device  node  "4, 130" via mknod /dev/ttyS2 c 4 130
36       would cause line ttyS2 to be treated in this way.   Turning  on  bit  6
37       (adding  64)  to  the  minor device number via mknod /dev/ttyS2 c 4 194
38       enables RTS/CTS flow control.
39
40       The DHU-11 driver normally uses input silos and delays receiver  inter‐
41       rupts  by 20 milliseconds rather than taking an interrupt on each input
42       character.
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FILES

45       /dev/tty[S-Z][0-9a-f]
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SEE ALSO

48       tty(4)
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DIAGNOSTICS

51       dhu(%d,%d) NXM.  No response from UNIBUS on a  DMA  transfer  within  a
52       timeout  period.   This  has  never  been  observed  on a PDP-11 and is
53       believed to be a carryover from the VAX driver when it was ported.   It
54       is not serious.
55
56       dhu%d %d overruns.  The character input silo overflowed before it could
57       be serviced.  This message is printed only at line  close  time  rather
58       than  on  each overrun error.  Kernel printf's are not interrupt driven
59       and caused more overruns by blocking interrupts for lengthy periods  of
60       time.
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NOTES

63       The  driver  currently does not make full use of the hardware capabili‐
64       ties of the DHU-11, for dealing with  XON/XOFF  flow-control  or  hard-
65       wired lines for example.
66
67       The 4 40-way cables are a pain.
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713rd Berkeley Distribution        May 31, 1997                           DHU(4)