dhb(4)							     Kernel Interfaces Manual							    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 constraints 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)