Programming
4-9
Numeric Consistency
Numeric consistency, or data consistency, refers to communications between the XVME
689-VR7 and the VMEbus in which the byte-ordering scheme described above is
maintained during the transfer of a 16-bit or 32-bit quantity. Numeric consistency is
achieved by setting the XVME 689-VR7 buffers to pass data straight through, which
allows the Universe chip to perform address-invariant byte-lane swapping. Numeric
consistency is desirable for transferring integer data, floating-point data, pointers, etc.
Consider the long word value
12345678h
stored at address
M
by both the XVME 689-
VR7 and the VMEbus, as shown in Figure 4-3.
Figure 4-3 Maintaining Numeric Consistency
Due to the Universe chip, the data must be passed straight through the byte-swapping
hardware. To do this, maintaining numeric consistency, enable the straight-through
buffers by setting bits 6 and 7 of the Flash Paging and Byte Swap register (register 234h)
to
1
(see p. 2-4).
Note
With the straight-through buffers enabled, the XVME 689-VR7 does not
support unaligned transfers. Sixteen-bit or 32-bit transfers must have an
even address.
Summary of Contents for XVME-689-VR7
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