Motorola MVME172 - Manual (Page 105)

LCSR Programming Model
http://www.mcg.mot.com/literature 2-27
2
A VMEbus slave map decoder is programmed by loading the starting
address of the segment into the starting address register and the ending
address of the segment into the ending address register. If the VMEbus
address modifier codes indicate an A24 VMEbus address cycle, then the
upper eight bits of the VMEbus address are forced to zero before the
compare. The address modifier select register should be programmed for
the required address modifier codes. A VMEbus slave map decoder is
disabled when the address modifier select register is cleared.
The address translation registers allow local resources to have different
VMEbus and local bus addresses. Only address bits A31 through A16 may
be modified.
The address translation registers also provide the upper eight local bus
address lines when an A24 VMEbus cycle is used to accesses a local
resource. The address translation register should be programmed with the
translated address and the address translation select register should be
programmed to enable the translated address. If address translation is not
desired, then the address translation registers should be programmed to
zero.
The address translation address register and the address translation select
register operate in the following way: If a bit in the address translation
select register is set, then the corresponding local bus address line is driven
from the corresponding bit in the address translation address register. If the
bit is cleared in the address translation select register, then the
corresponding local bus address line is driven from the corresponding
VMEbus address line. The most significant bit of the address translation
select register corresponds to the most significant bit of address translation
register and to A32 of the local bus and A32 of the VMEbus.
In addition to the address translation method previously described, the
VMEchip2 used on the MVME166/167/187 includes an adder which can
be used for address translation. When the adder is enabled, the local bus
address is generated by adding the offset value to the VMEbus address
lines VA<31..16>. The offset is the value in the address translation/offset
register. If the VMEbus transfer is A24, then the VMEbus address lines
VA<31..24> are forced to 0 before the add. The adders are enable by
setting bit 11 for map decoder 1 and bit 27 for map decoder 2 in register