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Hardware Configuration and Installation
When installed in Slot 0, the VXI-MXI becomes the VMEbus System Controller (set by slide
switches S1 and S8). As a VMEbus System Controller, it has VMEbus Data Transfer Bus Arbiter
(PRI ARBITER) circuitry that accepts bus requests on all four VMEbus request levels, prioritizes
the requests, and grants the bus to the highest priority requester. As VMEbus System Controller,
the VXI-MXI also drives the 16-MHz VMEbus system clock by an onboard 16-MHz oscillator with
a 50% ±5% duty cycle.
The VXI-MXI also performs VMEbus BTO functions as described in the following section. The
setting of the VME BTO Chain Position jumper block determines how to control these functions.
As required by the VXIbus specification for a Slot 0 device, the VXI-MXI drives the 10-MHz
signal, CLK10, on a differential ECL output. This is controlled by the CLK10 Source Select
jumpers at locations W9 and W10. The Slot 0 setting of the CLK10 Source Select jumpers cause
the VXI-MXI to drive CLK10 on the backplane. When configured for Non-Slot 0, the VXI-MXI
instead receives the CLK10 signal.
Warning:
Configuring more than one VXIbus device to drive the CLK10 lines can damage the
VXIbus backplane or the CLK10 drivers on the VXIbus devices.
VMEbus BTO
The VMEbus Bus Timeout (BTO) is a watchdog timer for transfers on the VMEbus Data Transfer
Bus. After a specified amount of time (usually user-configurable), the BTO circuitry terminates a
VMEbus cycle if no slave has responded. The VXI-MXI must provide the VMEbus BTO to
function properly because, when a MXIbus cycle is involved, the VMEbus timeout must be
disabled and the MXIbus BTO enabled. You should disable the BTO of any other BTO module
residing in the mainframe. If this is not possible, set it to its maximum setting to give the MXIbus
cycles as much time as possible to complete.
VXI Logical Address
Each device in a VXIbus/MXIbus system is assigned a unique number between 0 and 254. This
8-bit number, called the logical address, defines the base address for the VXI configuration
registers located on the device. With unique logical addresses, each VXIbus device in the system is
assigned 64 bytes of configuration space in the upper 16 kilobytes of A16 space.
Some VXIbus devices have dynamically configurable logical addresses. These devices have an
initial logical address of hex FF, which indicates that they can be dynamically configured. While
the VXI-MXI does support dynamic configuration of VXI devices within its mainframe, it is itself a
statically configured device and is preset at the factory with a VXI logical address of 1.
The AT-MXI is designated as the VXIbus Resource Manager (RM). As defined by the VXIbus
specification, the RM in a VXI system has a logical address of 0.
Ensure that no other statically configurable VXIbus devices have logical addresses of either 0 or 1.
If they do, change the logical address settings of the other devices so that every device in the system
has a unique associated logical address.
VXI-AT2023/NI-VXI ISC 386/ix Getting Started
2-18
© National Instruments Corporation
Chapter 2
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