Motorola MVME172 manual Programming the VMEbus Slave Map Decoders

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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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