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dhb(4)									dhb(4)

Name
       dhb - DHB32 communications multiplexer

Syntax
       device dmb0 at vaxbi? node? flags 0x????
	    vector dmbsint dmbaint dmblint

Description
       A  DHB32	 device provides 16 asynchronous communication lines with full
       modem control.  The DHB32 and the DMB32 share a common software	device
       driver.	 For  this reason, the configuration line is the same for both
       the DHB32 and DMB32.

       Each line attached to a DHB32 serial line port behaves as described  in
       Input  and  output for each line can 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  should  be
       treated	as a hardwired connection with carrier always present.	If bit
       i of flags is not set, the line will operate under full modem  control.
       Modem  lines will operate in accordance to the CD (carrier detect), DSR
       (data set ready) and CTS	 (clear	 to  send)  leads.   Thus,  specifying
       ``flags	0x0004''  in  the  specification  of would cause line 2 on the
       DHB32 to be treated as hardwired with carrier always present.  In  this
       example, the remainder of the lines will be modem control lines.

Diagnostics
       dmbinit: async lines unavailable
       This  message  is  produced  at system boot time if the DHB32 fails its
       internal self test indicating that the asynchronous lines  have	failed
       to configure.

       dmb%d: fifo overflow
       The  character input fifo overflowed before it could be serviced.  This
       can happen if the CPU is running with elevated priority for too long  a
       period  of  time.  Overflow errors may indicate that configuration con‐
       straints have been reached.

       dmb%d: DMA Error. tbuf = 0x%x
       A DMA output transfer failed.  This problem can result  from  a	memory
       error  or  an invalid pte (page table entry).  For a description of the
       error code in the ``tbuf'' register. See the DHB32 documentation.

       dmb%d: DMB Hardware Error. TX.DMA.START failed
       The failed to clear the start bit.  Normally, this is cleared to signal
       that a DMA transfer has completed.

       dmb%d: Modem Error. tbuf = 0x%x
       Indicates  a  problem  with a modem or its cable.  For a description of
       the error code in the ``tbuf'' register. See the DHB32 documentation.

       dmb%d: Internal Error. tbuf = 0x%x
       Indicates that the DHB32 detected an internal error.  For a description
       of the error code in the ``tbuf'' register. See the DHB32 User Guide.

Files
       (modem lines only)

See Also
       tty(4), MAKEDEV(8), dmbsp(4)

									dhb(4)

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