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The Base Address
To access a register, you must specify the register address in either hexadecimal or decimal. The register
address consists of a base address plus a register offset. The base address depends on whether the A16
address space is accessed via the Series C E1405 Command Module or via some other controller.
A16 Address Space when not using the E1405 Command Module
When the Command Module or Mainframe is not part of your VXIbus system (ie., you are using an
embedded controller), the module's base address is computed by adding the following to the controller
specific offset:
hexadecimal
C000h + (LADDR * 64)h
where C000h (49,152) is the starting location of the register addresses, LADDR is the module's logical
address, and 64 is the number of address bytes per register-based module. For example, the module's
factory set logical address is 136. If this address is not changed, the module will have a base address
consisting of the controller specific offset with the following added to it:
hexadecimal
C000h + (136 * 64)h
C000h + 2200 = E200h
A16 Address Space Using the Command Module
When the A16 address space is accessed via the Command Module, the module's base address is
computed as:
hexadecimal
1FC000h + (LADDR * 64)h
where 1FC000h (2,080,768) is the starting location of the register addresses, LADDR is the module's
logical address, and 64 is the number of address bytes per register-based module. For example, the
module's factory set logical address is 136. If this address is not changed, the module will have a base
address of:
hexadecimal
1FC000h + (136 * 64)h
1FC000h + 2200h = 1FE200h
Register Offset
The register offset is the register's location in the block of 64 address bytes (see Table 2-1). For example,
the module's Command register has an offset of 22h. When writing a value to this register, this offset is
added to the base address to form the register address:
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decimal
49,152 + (LADDR * 64)
decimal
49,152 + (136 * 64)
49,152 + 8704 = 57,856
decimal
2,080,768 + (LADDR * 64)
decimal
2,080,768 + (136 * 64)
2,080,768 + 8704 = 2,089,472
Register Maps 3-3
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