Chapter 5
System Configuration
VME-MXI-2 User Manual
5-4
© National Instruments Corporation
The recommended way to set up your system is to fill up Level 1
MXIbus links before adding additional levels. System performance
decreases as you increase the number of levels to the system because
each level requires additional signal conversion. Also keep in mind
these basic rules for VME-MXI-2 installation as you decide where to
install your VME-MXI-2 interfaces:
•
The VMEbus bus timeout unit must be on a VME-MXI-2.
•
Multiple VME-MXI-2 interfaces in a mainframe require a
dedicated user-defined pin.
The address mapping windows on the VME-MXI-2 can be configured
to have a Base/Size format or a High/Low format. The CMODE bit in
the VME-MXI-2 Control Register (VMCR) selects which format the
mapping windows use.
Base/Size Configuration Format
Each address mapping window on a VME-MXI-2 interface has Base
and Size parameters associated with it when the CMODE bit in the
VME-MXI-2 Control Register (VMCR) is cleared. The Base bits
define the base address for the window, and the Size bits indicate the
number of Base bits that are significant. Replacing the insignificant bits
with zeros gives the actual base address of the window. In other words,
the Base and Size define a range of addresses that are in the window.
A Direction bit is also included to indicate whether the defined range
of addresses are mapped into or out of the VMEbus mainframe.
Table 5-1 shows which bits are compared for each Size setting and
the resulting address range in hex if Base is set to 0 and 55 hex.
Figure 5-3 further illustrates the number of bits of the Base that are
compared for each Size value. Notice that if Size = 0, no bits are
compared. Figure 5-4 shows the address range allocation for different
Size values.
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