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

6       dh - DH-11/DM-11 communications multiplexer
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SYNOPSIS

9       /sys/conf/SYSTEM:
10            NDH  dh_units  # DH11; NDH is in units of boards (16 each)
11            NDM  dm_units  # DM11; NDM is in units of boards (16 each)
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13       /etc/dtab:
14            #Name Unit# Addr   Vector Br Handler(s)      # Comments
15            dm    ?     170500 310    4  dmintr          # dm11 dh modem control
16            dh    ?     160020 320    5  dhrint  dhxint  # dh11 terminal mux
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18       major device number(s):
19            raw: 3
20       minor device encoding:
21            bits 0017 specify line on DH unit
22            bits 0060 specify DH unit
23            bit  0100 specify RTS/CTS (``hardware'') flowcontrol
24            bit  0200 specifies non-blocking open (``CD always on'')
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DESCRIPTION

27       A  dh-11  provides  16  communication  lines; dm-11's may be optionally
28       paired with dh-11's to provide modem control for the lines.   If  there
29       are  fewer  dm-11's  than dh-11's, the dm-11's are assumed to be paired
30       with the first dm_units dh-11's.
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32       Each line attached to the DH-11 communications multiplexer  behaves  as
33       described  in tty(4).  Input and output for each line may independently
34       be set to run at any of 16 speeds; see tty(4) for the encoding.
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36       Bit 0200 of the minor device number for DH lines may be set to say that
37       a  line  is not properly connected, and that the line should be treated
38       as hard-wired with carrier always present.  Thus creating  the  special
39       character device node "3, 130" via mknod /dev/ttyh2 c 3 130 would cause
40       line ttyh2 to be treated in this way.  Bit 0100  of  the  minor  device
41       number  enables  RTS/CTS (also called ``hardware'') flow control. It is
42       enabled by adding 64 to the minor device number: mknod /dev/ttyh2  c  3
43       194
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45       The  dh  driver  monitors the rate of input on each board, and switches
46       between the use of  character-at-a-time  interrupts  and  input  silos.
47       While  the  silo  is  enabled  during  periods of high-speed input, the
48       driver polls for input 30 times per second.
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FILES

51       /dev/tty[h-k][0-9a-f]
52       /dev/ttyd[0-9a-f]
53       /dev/MAKEDEV        script to create special files
54       /dev/MAKEDEV.local  script to localize special files
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SEE ALSO

57       tty(4), dtab(5), autoconfig(8)
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DIAGNOSTICS

60       dh%d NXM.  No response from UNIBUS on a dma transfer within  a  timeout
61       period.   This  has  never been observed on a PDP-11 and is a carryover
62       from the VAX driver when it was ported.  It is not serious.
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64       dh%d %d overruns.  The character input silo overflowed before it  could
65       be  serviced.   This message is only printed at line close time.  It is
66       not serious but does indicate that the system was not able to  keep  up
67       with the data flow.
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713rd Berkeley Distribution        May 31, 1997                            DH(4)
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