Chapter 3
VME-MXI-2 Configuration and Installation
© National Instruments Corporation
3-3
VME-MXI-2 User Manual
VMEbus A16 Base Address
The VME-MXI-2 requires 64 bytes of A16 space for its configuration
registers. It uses the logical address scheme of the VXIbus
specification, in which each device is assigned an 8-bit value called the
logical address. This logical address allocates 64 bytes of space to the
device within the upper quarter of A16 space. The VME-MXI-2 cannot
be configured to locate its registers in the lower three quarters of A16
space. The A16 base address of the VME-MXI-2 will be address lines
15 and 14 high with address lines 13 through 6 matching the logical
address of the VME-MXI-2, and address lines 5 through 0 low. In other
words, the A16 base address of the VME-MXI-2 module’s
64-byte register set is as calculated below:
base address = C000 hex + (logical address) * 40 hex
The factory-default logical address for the VME-MXI-2 is 1, which
locates the registers in the range C040 hex to C07F hex. You can
change the logical address of the VME-MXI-2 by changing the setting
of the 8-bit DIP switch at location designator U20. The ON position of
the DIP switch corresponds to a logic value of 0, and the OFF position
corresponds to a logic value of 1. Allowable logical addresses for the
VME-MXI-2 range from 1 to 254 (FE hex). Verify that no other
devices in your system use the A16 address space for the VME-MXI-2.
If possible, configure all other VMEbus A16 devices to be located
within the lower three quarters of A16 space. Also, when setting base
addresses, keep in mind the grouping requirements set by the system
hierarchy. See either Chapter 5, System Configuration, or VXI-6, the
VXIbus Mainframe Extender Specification, for more information on
setting base addresses on a multimainframe hierarchy.
Figure 3-2 shows switch settings for A16 base address C040 hex and
F000 hex.
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