Chapter 6
VXIplug&play for the VME-MXI-2
VME-MXI-2 User Manual
6-4
© National Instruments Corporation
If you select Software for this option, you can then use the Logical
Address control to select a logical address within the range of 1 to 254.
If you use this option, the hardware switch setting has no effect and you
must use the VME-MXI-2 soft front panel to change the logical
address.
Address Space and Requested Memory
The VME-MXI-2 requires at least 16 KB of address space in A24
space or at least 64 KB in A32 space. Use the Address Space control
to select whether you want to use A24 space or A32 space. Use the
Requested Memory control to set the amount of memory space that
the VME-MXI-2 will require. You can select up to 8 MB in A24 space
and up to 2 GB in A32 space.
These controls are necessary if you change the amount of DRAM
installed on the VME-MXI-2. The amount of memory you set with
the Requested Memory control should match the amount of DRAM
installed on the VME-MXI-2. If no DRAM is installed, you should
set it to 16 KB. Notice that the smallest valid amount in A32 space is
64 KB.
Caution:
If you install DRAM into the VME-MXI-2, do not attempt to use the
first 4 KB of memory space. This 4 KB space maps to the registers on
the VME-MXI-2 and does not access onboard DRAM. Accessing this
region will cause your VME-MXI-2 to behave incorrectly.
If you do not want to lose 4 KB of DRAM you can get around this
limitation by setting the Requested Memory control to double the
amount that is installed on the VME-MXI-2, since the DRAM is
aliased throughout the remainder of the requested memory space. The
DRAM should then be accessed in the upper half of the requested
memory space.
A16 Write Post and A24/A32 Write Post
The VME-MXI-2 can increase performance with its capability to post
write cycles from both the MXIbus and the VMEbus. Write cycles
should be posted only to devices that cannot return a BERR signal,
because the BERR will not be reported to the originating master. Use
the control appropriate for either A16 write posting or A24/A32 write
posting. For either control, the options are Enabled and Disabled. By
default, both options are disabled.
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