Service manual

The <REFERENCE>(XBIA) contains the <REFERENCE>(XMI) Corner,
the register files, <REFERENCE>(XMI) required registers, <REFERENCE>(XBIA)-
specific registers, page map registers, and the control sequencers for the
<REFERENCE>(XMI) interface.
The <REFERENCE>(XBIB) contains the BIIC interface chip, interconnect
drivers, control sequencers to handle the control of the data transfer, status
bits to and from the <REFERENCE>(XBIA) module’s register files and
the BIIC, <REFERENCE>(XBIB)-specific registers, decode logic for direct
memory access (DMA) operation, and VAXBI clock-generation circuitry.
The <REFERENCE>(XBIA) and <REFERENCE>(XBIB) modules are
connected by four cables of 30 wires each. These 120 wires make up
the IBUS, which transfers data and control information between the two
modules.
The <REFERENCE>(xbi_plus) uses I/O and DMA transactions to exchange
information. I/O transactions originate from the <REFERENCE>(XYP)
or <REFERENCE>(XRP) module(s) and are presented to the <REFER-
ENCE>(xbi_plus) from the <REFERENCE>(XMI) bus with the processor as
the <REFERENCE>(XMI) commander and the <REFERENCE>(xbi_plus)
as the <REFERENCE>(XMI) responder.
DMA transactions originate from VAXBI nodes that select the <REFER-
ENCE>(xbi_plus) as the VAXBI slave. These are read or write transactions
targeted to <REFERENCE>(XMI) memory space or are VAXBI-generated
interrupt transactions that target a <REFERENCE>(xyp) or <REFER-
ENCE>(XRP) module. For DMA transactions, the <REFERENCE>(xbi_
plus) is the <REFERENCE>(XMI) commander, and the <REFERENCE>(XMA)
module is the <REFERENCE>(XMI) responder.
The <REFERENCE>(xbi_plus) can be both a master and a slave on
the VAXBI. As a master, it carries out transactions requested by
its <REFERENCE>(XMI) devices. As a slave, it responds to VAXBI
transactions that select its node.
DWMBB I/O Adapter 7–9