Motorola MVME172 User Manual download pdf (Page 104)

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VMEchip2

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.

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Motorola MVME172 User Manual Page 104