User`s guide

The VAX 6000 Platform Overview
1.7 DWMBB I/O Adapter
The DWMBB adapter provides an information path between the
XMI bus and I/O devices on the VAXBI bus. The DWMBB consists
of two modules: the DWMBB/A module and the DWMBB/B module.
The DWMBB/A module resides on the XMI bus, and the DWMBB/B
module resides on the VAXBI bus. Four 30-pin cables, which make
up the IBUS, connect the two modules.
Figure 1–7 DWMBB Adapter Block Diagram
DWMBB/A
MODULE
LOGIC
XMI
CORNER
VAXBI
CORNER
(BIIC)
IBUS
VAXBIXMI
T1043 MODULE
T2018 MODULE
msb-0062A-90
DWMBB/B
MODULE
LOGIC
Figure 1–7 shows the two modules of the DWMBB adapter, which serve as
the interface between the XMI and VAXBI buses. The DWMBB/A and the
DWMBB/B modules are connected by the IBUS, made up of four 30-wire
cables, which transfer data and control information between the two.
The DWMBB uses I/O and DMA transactions to exchange information. I/O
transactions originate from the CPU module(s) and are presented to the
DWMBB from the XMI bus with the processor as the XMI commander and
the DWMBB as the XMI responder.
DMA transactions originate from VAXBI nodes that select the DWMBB
as the VAXBI slave. These are read or write transactions targeted to XMI
memory space or are VAXBI-generated interrupt transactions that target a
CPU module. For DMA transactions, the DWMBB is the XMI commander,
and the memory module is the XMI responder.
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