User manual

Chapter 6 System Configuration

Planning a VXIbus/MXIbus System A16 Address Map

The VXIbus specification does not define a method for dynamically

determining the amount of A16 space each device requires. The

specification defines the upper 16 KB of A16 space for VXIbus device

configuration registers. In most cases, the lower 48 KB of A16 space

are used for VMEbus devices installed in the VXIbus system. In a

VXIbus/MXIbus system, A16 space is defined as that lower 48 KB of

the A16 address space. As system integrator, you must determine the

A16 address requirements for your VXIbus/MXIbus system and define

the A16 space ranges needed as foreign devices to the system RM.

You should configure the A16 resources for your VMEbus boards in

the lower 48 KB (0000 through BFFF hex) of A16 space, so that you

do not interfere with VXIbus configuration space. The logical address

mapping window is then used for mapping configuration space for

VXIbus devices, and the A16 mapping window is used for mapping

configuration space for VMEbus devices.

When using Base/Size windowing formats, the minimum size of

an A16 window is 512 B and the maximum size is 48 KB (window

size = 0). Setting an A16 window address range in the upper 16 KB of

A16 space (A15 = 1, A14 = 1) is not allowed, because it would conflict

with the logical address space. Table 6-3 shows the A16 allocation

sizes used for Base/Size systems.

Table 6-3. Amount of A16 Space Allocated for all Size Values

Size Amount of A16 Space Allocated (in Bytes)

7 512 B

6 1 KB

5 2 KB

4 4 KB

3 8 KB

2 16 KB

1 32 KB

0 48 KB (All A16 space)