Table of Contents
Advertisement
LCSR Programming Model
You program a VMEbus slave map decoder by loading the starting address
2
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 0 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 access 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 0.
The address translation address register and the address translation select
register operate in the following way: If you set a bit in the address
translation select register, then the corresponding bit in the address
translation address register drives the appropriate local bus address line. If
you clear the bit in the address translation select register, then the
corresponding VMEbus address line drives the appropriate local bus
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 as used on the MVME1X7P 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 addition. The adders are enabled by
setting bit 11 for map decoder 1 and bit 27 for map decoder 2 in register
http://www.motorola.com/computer/literature
2-27
Advertisement
Table of Contents
