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Determining a
Module's A16 Base
Address
Addressing A16
Register
60 Register Programming Information
To access a register in A16 memory, you must specify a hexadecimal or
decimal register address. The address consists of a base address plus a
register offset. The A16 base address depends on whether or not you are
using an HP E1406 Command Module.
When using an HP E1406 Command Module, the base address is computed
as:
1FC000 + (LADDR
h
or (decimal)
2,080,768 + (LADDR * 64)
Where:
1FC000
(2,080,768) is the starting location of the VXI A16 addresses,
h
LADDR is the module's logical address
40
(64) is the number of address bytes per register-based device.
h
For example, if the M-Module has a logical address of 78
base address becomes:
1FC000h + (78
* 40
h
or (decimal)
2,080,768 + (120 * 64) = 2,080,768 + 7680 = 2,088,448
When an HP Command Module is not a part of your VXIbus system (see
Figure 4-4), the M-Module's base address is computed as:
C000
+ (LADDR
* 40
h
h
or (decimal)
49,152 + (LADDR * 64)
Where:
C000
(49,152) is the starting location of the register addresses,
h
LADDR is the module's logical address
40
(64) is the number of address bytes per VXI device.
h
For example, if the M-Module has a logical address of 78
base address becomes:
C000
+ (78
* 40
) = C000
h
h
h
or (decimal)
49,152 + (120 * 64) = 49,152 + 7680 = 56,832
As shown in Figure 4-4, VXI register for an M-Module (installed in an HP
E2251 Carrier) are mapped into A16 address space. To access one of these
registers, add the A16 base address to the register offset. For example, an
M-Module's VXI Status/Control register has an offset of 04
register (assuming the system does not have an HP E1406 Command
Module), use the register address:
1FDE00
+ 04
= 1FDE04
h
h
or (decimal)
2,088,488 + 4 = 2,088,452
* 40
)
h
) = 1FC000
+ 1E00
= 1FDE00
h
h
h
)
h
+ 1E000
= DE00
h
h
h
(120) the A16
h
h
(120) the A16
h
h
. To access this
h
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