dh man page on Ultrix

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dh(4)				  Unsupported				 dh(4)

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

Syntax
       device dh0 at uba? csr 0160020 flags 0x???? vector dhrint dhxint
       device dm0 at uba? csr 0170500 flags 0x???? 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 Input and output for each line may independently be set to
       run at any of 16 speeds; see for the encoding.

       Bit i of flags may be specified for a to say that a line is  not	 prop‐
       erly  connected, and that the line should be treated as hard-wired with
       carrier always present.	Thus specifying ``flags 0x0004'' in the speci‐
       fication of dh0 would cause line ttyh2 to be treated in this way.

       The  driver normally uses input silos and polls for input at each clock
       tick (10 milliseconds) rather than taking an interrupt  on  each	 input
       character.

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.  If the Berknet is running on a line at high speed
       (for example, 9600 baud), there is only 1/15th of a second of buffering
       capacity	 in  the  silo, and overrun is possible.  This may cause a few
       input characters to be lost to users and a network packet is likely  to
       be corrupted, but the network will recover.  It is not serious.

Files
See Also
       tty(4)

				      VAX				 dh(4)
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