Motorola MVME172 - Manual (Page 104)

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VMEchip2
2
Programming the VMEbus Slave Map Decoders
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 and starting and ending address
registers should be programmed first, and then the map decoders should be
enabled by programming the address modifier select registers.