DHV(4)		    UNIX Programmer's Manual		   DHV(4)



NAME
     dhv - DHV-11 communications multiplexer

SYNOPSIS
     /sys/conf/SYSTEM:
	  NDHV _d_h_v__u_n_i_t_s # DHV11

     /etc/dtab:
	  #Name Unit# Addr   Vector Br Handler(s)      # Comments
	  dhv	?     160440 310    5  dhvrint dhvxint # dhv terminal mux

     major device number(s):
	  raw: 24
     minor device encoding:
	  bits 0007 specify line on DHV unit
	  bits 0070 specify DHV unit
	  bit  0100 specifies RTS/CTS (``hardware'') flowcontrol
	  bit  0200 specifies non-blocking open (``CD always on'')

DESCRIPTION
     A DHV-11 provides 8 communication lines.

     Each line attached to the DHV-11 communications multiplexer
     behaves as described in _t_t_y(4).  Input and output for each
     line may independently be set to run at any of 13 speeds (50
     and 200 baud are not available).  While 38400 is available
     the underlying hardware is not fast enough to handle it and
     there will be pauses/gaps between characters.

     Bit _0_2_0_0 of the minor device number for DHV lines may be set
     to say that a line is not properly connected, and that the
     line should be treated as hard-wired with carrier always
     present.  Thus creating the special character device node
     "4, 130" via _m_k_n_o_d /_d_e_v/_t_t_y_S_2 _c _4 _1_3_0 would cause line ttyS2
     to be treated in this way.  Turning on bit 6 in the minor
     device number via _m_k_n_o_d /_d_e_v/_t_t_y_S_2 _c _4 _1_9_4 would enable
     RTS/CTS flow control.

     The DHV-11 has an input silo but does not have the programm-
     able receiver delay that the DHU (and DHQ) have.  Thus sys-
     tem services more interrupts (i.e. gets fewer characters per
     interrupt on average) with a DHV-11 than with a DHQ (in DHU
     mode).

FILES
     /dev/tty[S-Z][0-9a-f]

SEE ALSO
     tty(4)

DIAGNOSTICS
     dhv%d,%d NXM.  No response from QBUS on a DMA transfer



Printed 11/26/99	  May 31, 1997				1






DHV(4)		    UNIX Programmer's Manual		   DHV(4)



     within a timeout period.  This error has never been observed
     on a PDP-11 and is a carryover from the VAX driver when that
     was ported to 2BSD.

     dhv%d diag %o.  Diagnostic information from the DHV11.  This
     has never been observed.  The DHV-11 hardware manual will be
     required to decode the value printed out.

     dhv%d: %d overruns.  The character input silo overflowed
     before it could be serviced.  This message is printed only
     when the line is closed.  By only printing this when the
     line is closed further silo overruns are avoided (kernel
     printf statements are not interrupt driven).

NOTES
     The DHV lacks the receiver delay that the DHU (and DHQ)
     have.  Thus it is extremely easy (indeed it's almost certain
     at higher data rates) for a DHV-11 to enter an interrupt per
     character mode and use 70-80% of the cpu.




































Printed 11/26/99	  May 31, 1997				2