DZ(4)                 OpenBSD Programmer's Manual (PMAX)                 DZ(4)

NAME
     dz - dc659, dc7085 DZ11-on-a-chip serial communications interface

SYNOPSIS
     dz0 at ioasic?
     dz0 at mainbus
     dz1 at mainbus
     dz2 at mainbus

DESCRIPTION
     The dz driver provides support for Digital's dc7085 four-port serial com-
     munications chip.  The dz driver supports dc7085 hardware on attached to
     the following parent devices:

           mainbus  baseboard device on DECstation 2100, 3100, and 5100, and
                    optional expansion devices on the 5100.
           ioasic   baseboard device on DECstation 5000/200.
           vsbus    baseboard devices on the VAXstation 2000 and 3100.

     The dz device is in essence a single-chip clone of the DZ-11.  The DZ-11
     hardware design severely constrains performance.  One small input silo is
     shared across all input ports.  The dz hardware does not interrupt on mo-
     dem transitions; instead, they are detected via polling.  Only two lines
     on a baseboard dz device  have any modem control signals; the other two
     lines are wired for a keyboard and mouse.

     On some implementations (e.g., DECstation 3100), the hardware does not
     bring out modem flow-control signals to the bulkhead. Only modem carrier
     transition are provided. This is adequate for Unix dialin and dialout de-
     tection, but without hardware flow control, the dz device is prone to
     overruns when used for serial-line protocols.

     The DECstation 5000/200 dz hardware provides full modem control on both
     bulkhead RS-232 ports and is less prone to overrun.

BUGS
     The 19200 speed on all dz devices is actually implemented as 19800, pre-
     sumably for bug-compatibility with the original DZ-11.  This is a hard-
     ware feature and cannot be corrected in software.  Many serial devices at
     19200 fail to interoperate with the dz at its 19800 speed setting.

     The DECstation 5000/200 can set a bit in the system register to allow the
     dz to run at 38400, but this applies to all four lines and disables the
     19200 speed on all four lines. This feature is not currently supported.

     The dz driver should be merged into a single driver supporting the origi-
     nal DZ-11, DZ-32, and Qbus DZV-11 and DZQ-11 clones.

HISTORY
     The dz driver first appeared in 4.4BSD/pmax. This manual page first
     appeared in NetBSD 1.2.  Due to a name conflict the driver was renamed
     from dc to dz in OpenBSD 2.7.

OpenBSD 2.9                    February 20, 1998                             1
