Appendix D
Differences and Incompatibilities between the VME-MXI and the VME-MXI-2
© National Instruments Corporation
D-3
VME-MXI-2 User Manual
VXIbus Model Code
The VXIbus Device Type Register (VDTR) on the VME-MXI-2
returns a different model code than the VME-MXI because it includes
new capabilities and is not an identical replacement for the VME-MXI.
Required Memory Space
The VME-MXI-2 register set is too large to fit in its 64-byte VXIbus
configuration area. In addition, you can install onboard DRAM on the
VME-MXI-2. For both of these reasons the VME-MXI-2 requests at
least 16 KB of either A24 or A32 space, whereas the VME-MXI was
an A16-only device. As a result, the VME-MXI-2 has a VXIbus Offset
Register (VOR), a Required Memory field in the VXIbus Device Type
Register (VDTR), and an A24/A32 ENABLE bit in the VXIbus
Status/Control Register (VSR/VCR).
Sysfail Inhibit
The VME-MXI-2 provides a Sysfail Inhibit bit in the VXIbus
Status/Control Register (VSR/VCR) to prevent it from asserting
the SYSFAIL* signal as defined by the VXIbus specification. The
first-generation VME-MXI did not.
VME-MXI-2 Status/Control Register (VMSR/VMCR)
The RMWMODE bit is no longer implemented. The VME-MXI-2 uses
the MXI-2 bus CONVERT* signal to determine how to pass a MXIbus
access to the VMEbus. When CONVERT* is not asserted, MXIbus
block and RMW accesses are passed to the VMEbus unmodified. When
CONVERT* is asserted, the VME-MXI-2 converts MXIbus block and
indivisible accesses into single VMEbus accesses.
The Long MXIbus System Controller Timeout bit (LNGMXSCTO) is
no longer implemented. The MXIbus timer of the VME-MXI-2 is
programmable in the EEPROM and covers an even broader range of
times than the MXIbus timer of the VME-MXI.
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