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VMEchip2
Programming the VMEbus Slave Map Decoders
2
2-28
This section includes programming information for the VMEbus to
local bus map decoders.
The VMEbus to local bus interface allows off-board VMEbus
masters access to local onboard resources. The address of the local
resources as viewed from the VMEbus is controlled by the VMEbus
slave map decoders, which are part of the VMEbus to local bus
interface. Two VMEbus slave map decoders in the VMEchip2 allow
two segments of the VMEbus to be mapped to the local bus. A
segment may vary in size from 64KB to 4GB in increments of 64KB.
Address translation is provided by the address translation registers
which allow the upper 16 bits of the local bus address to be
provided by the address translation address register rather than the
upper 16 bits of the VMEbus.
Each VMEbus slave map decoder has the following registers:
address translation address register, address translation select register,
starting address register, ending address register, address modifier select
register, and attribute register. The addresses and bit definitions of
these registers are shown in the following tables.
The VMEbus slave map decoders described in this section are
disabled by local reset, SYSRESET, or power-up reset. Caution
must be used when enabling the map decoders or when modifying
their registers after they are enabled. The safest time to enable or
modify the map decoder registers is when the VMEchip2 is
VMEbus master. The following procedure should be used to
modify the map decoder registers: Set the DWB bit in the LCSR and
then wait for the DHB bit in the LCSR to be set, indicating that
VMEbus mastership has been acquired. The map decoder registers
can then be modified and the VMEbus released by clearing the
DWB bit in the LCSR. Because the VMEbus is held during this
programming operation, the registers should be programmed
quickly with interrupts disabled.
The VMEbus slave map decoders can be programmed, without
obtaining VMEbus mastership, if they are disabled and the
following procedure is followed: The address translation registers
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