VXI 320222-01 Chapter 5 Programming Considerations

Chapter 5Programming 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.

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.

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.