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© National Instruments Corporation 5-1 VXI-MXI User Manual
Chapter 5
Programming Considerations
This chapter explains important considerations for programming and configuring a VXIbus/
MXIbus system using VXI-MXIs.
Note: Detailed descriptions of all register bits can be found in Chapter 4, Register
Descriptions.
System Configuration
In a MXIbus system, MXIbus address space is partitioned between MXIbus devices. A MXIbus
device is any device having a MXIbus interface. MXIbus devices can be VXIbus mainframes,
personal computers (PCs), or stand-alone instruments. The MXIbus memory map is the same for
all devices in the VXIbus/MXIbus system. Multiple VXIbus subsystems share one
VXIbus/MXIbus Resource Manager (RM). This multiframe RM performs all the VXIbus RM
functions and configures all VXI-MXIs in the system to partition the MXIbus address space.
A VXIbus/MXIbus system can be connected together to form any arbitrary tree topology. A tree
topology has no circular paths. Examples of tree topologies are shown in Figures 5-1 and 5-2.
The system in Figure 5-1 would not be a tree structure if a cable were added from the last
MXIbus device on Level 1 to the Root PC. Figure 5-2 would also be an illegal and circular
system if a cable were added to connect the two MXIbus devices on Level 1. At the root of the
tree is the multiframe RM. The root can be a VXIbus mainframe or a stand-alone device (for
example, a PC with a MXIbus interface) that can operate as the system RM.
All MXIbus devices have address windows that connect them to the MXIbus system address
map. MXIbus devices can be assigned space in any of four address spaces: A32, A24, A16 and
logical address space. Upon initialization, all windows are turned off, isolating all MXIbus
devices from each other. The multiframe RM scans the MXIbus links and VXIbus mainframes
for devices and configures the window registers on each MXIbus device in order to partition the
MXIbus address space among all devices.
Planning a VXIbus/MXIbus System Logical Address Map
The VXIbus/MXIbus system integrator is the person who configures all the VXIbus and MXIbus
devices and connects the system together. This chapter assumes that you are the system
integrator.
Before you begin setting the logical addresses of the devices in your VXIbus/MXIbus system,
you must determine the tree configuration of your system. The two basic configurations are the
MXIbus multiframe RM as an external PC with a MXIbus interface, as shown in Figure 5-1, or
the MXIbus multiframe RM in a VXIbus mainframe, as shown in Figure 5-2. The location of the
multiframe RM constitutes the root of the system tree. MXIbus links connected to the root of the
tree form levels of the tree. Notice that only one MXIbus link can be connected on the first level
below a root PC multiframe RM, while multiple MXIbus links can be connected on the first level
below a root VXIbus mainframe.