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Configuration and Installation Chapter 3
VXI-MXI User Manual 3-24 © National Instruments Corporation
MXIbus Termination
The MXIbus is a matched impedance bus and requires termination networks at the first and last
device in the MXIbus daisy-chain. These terminations minimize reflections caused by
impedance discontinuities at the ends of the cables. These termination networks are located at
the end device's MXIbus connectors and can be either external self-contained modules or internal
plug-in resistor packages. The VXI-MXI comes with terminating resistors installed. If you
prefer, you can replace them with external resistor packages for easy system reconfiguration.
Figure 3-20 shows an example of a daisy-chained MXIbus system, including terminators.
MXIbus System
Controller
PC/AT
VXI
Mainframe
VXI
Mainframe
VXI
Mainframe
MXIbus Cable
62-pin MXIbus Connectors
Downstream
Terminator
VXI-MXI
VXI-MXI
VXI-MXIVXI-MXI
Upstream
Terminator
VXI
Mainframe
Figure 3-20. MXIbus System
The VXI-MXI uses the TERMPWR connection on the MXIbus connector as the power source
for external MXIbus termination networks. TERMPWR is protected by a fuse that limits the
maximum current that can be drawn to 2A. The fuse is soldered on the module and is not user
replaceable.
Note: TERMPWR is not intended to provide power to any other device.
The VXI-MXI is shipped from the factory with terminating SIP resistor networks installed. If
the VXI-MXI will be the first or last device in the MXIbus daisy-chain and external terminating