Motorola MVME172 manual VMEchip2

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VMEchip2

Each of the four programmable local bus map decoders has a starting address, an ending address, an address modifier register with attribute bits, and an enable bit. The fourth decoder also has address translation registers. The addresses and bit definitions for these registers are in the tables below.

A local bus slave map decoder is programmed by loading the starting address of the segment into the starting address register and the ending address of the segment into the ending address register. The address modifier code is programmed in to the address modifier register. Because the local bus to VMEbus interface does not support VMEbus block transfers, block transfer address modifier codes should not be programmed.

The address translation register allows a local bus master to view a portion of the VMEbus that may be hidden by onboard resources or an area of the VMEbus may be mapped to two local address. For example, some devices in the I/O map may support write posting while others do not. The VMEbus area in question may be mapped to two local bus addresses, one with write posting enabled and one with write posting disabled. The address translation registers allow local bus address bits A31 through A16 to be modified. The address translation register should be programmed with the translated address, and the address translation select register should be programmed to enable the translated address. If address translation is not desired, then the address translation registers should be programmed to zero.

The address translation address register and the address translation select register operate in the following way. If a bit in the address translation select register is set, then the corresponding VMEbus address line is driven from the corresponding bit in the address translation address register. If the bit is cleared in the address translation select register, then the corresponding VMEbus address line is driven from the corresponding local bus address line. The most significant bit of the address translation select register corresponds to the most significant bit of address translation address register and to A32 of the local bus and A32 of the VMEbus.

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