Motorola MVME1X7P - Manual (Page 116)

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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 on-board 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. The upper 16 bits of the local bus address
come from the address translation address register rather than from the
upper 16 bits of the VMEbus address.
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 tables on the following pages list the addresses
and bit definitions of these registers.
The VMEbus slave map decoders described in this section are disabled by
local reset, SYSRESET
∗
, or power-up reset. Use caution 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.
To modify the map decoder registers, follow this procedure: 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.