Register Addressing
Register addresses for register-based devices are located in the upper 25%
of the VXI A16 address space. Every VXI device (up to 256) is allocated a
64 (40
16
) byte block of addresses. Figure D-1 shows the register address
location within the A16 address space.
The Base Address
When you are reading or writing to a register, a hexadecimal or decimal
address is specified. This address consists of a base address plus a register
offset.
The base address is computed as:
49,152+LADDR*64
or
C000
16
+LADDR
16
*40
16
where 49,152 (C000
16
) is the starting location of the register addresses,
LADDR is the module’s logical address, and 64 (40
16
) is the number of
address bytes per VXI device. For example, the HP E1413’s factory set
logical address is 24
10
(18
16
). If this address is not changed, the module
will have a base address of:
49,152+24*64
49,152+1,536=50,688
or
C000
16
+18
16
*40
16
C000
16
+600
16
=C600
16
336 Register-Based Programming
Appendix D
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