Chapter 4
Register Descriptions
© National Instruments Corporation
4-45
VME-MXI-2 User Manual
VMEbus A24/A32 Registers
Some of the registers on the VME-MXI-2 are accessible only within the A24 or A32
space that is allocated to the VME-MXI-2. The following are register descriptions of
some of these registers. See Table 4-2 for a register map of these registers. The table
gives the mnemonic, offset from the base address, access type (read only, write only, or
read/write), access size, and register name.
To enable access to the A24 or A32 space on the VME-MXI-2, first write the desired
base address to the VXIbus Offset Register (VOR), then set the A24/A32 ENABLE bit in
the VXIbus Control Register (VCR). Prior to these actions, the VME-MXI-2 will not
respond to any A24 or A32 access—only the A16 registers are available. Read the
VXIbus ID Register (VIDR) to determine the address space (either A24 or A32) to which
the VME-MXI-2 will respond. To determine the amount of space that the VME-MXI-2
requires, read the REQMEM [3:0] bits in the VXIbus Device Type Register (VDTR).
The base address of the VME-MXI-2 A24 or A32 space must be located on a boundary
of the size being requested. If you are using a VXIbus Resource Manager, this will be
done automatically and you can just read the VIDR and VOR to determine the address
space (A24 or A32) and base address at which the VME-MXI-2 is located. See the
register descriptions of the VIDR, VDTR, VCR, and VOR for more information.
These registers occupy the first 4 KB of address space allocated to the VME-MXI-2. Any
access to the VME-MXI-2 A24/A32 space beyond the first 4 KB (address offsets above
FFF hex) will map to the onboard DRAM SIMM sockets. The address offset shown in
each register description is the offset from the base A24/A32 address of the VME-MXI-2
as defined by the VIDR and VOR registers.
Most of these registers are used to configure the two onboard DMA controllers. The two
DMA controllers are identical to each other but are independent; they can be used
simultaneously without affecting the operation of each other. Because the registers for the
two DMA controllers are identical, this section describes only one set of registers, but the
descriptions apply to both DMA controllers. The registers for DMA Controller 1 begin at
offset D00 from the VME-MXI-2 module base A24/A32 address, while the registers for
DMA Controller 2 begin at offset E00 as shown in Table 4-2. For an example of how to
use the DMA controllers, refer to Appendix F, DMA Programming Examples.
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