Motorola MVME2600 Series Reference Manual page 200

Programming Model
Note that in addition to the programmed address, the first
1Mbyte of Block B also appears at $FFF00000 -
$FFFFFFFF if the rom_b_rv bit is set.
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Also note that the combination of ROM_B_BASE and
rom_b_siz should never be programmed such that ROM
Block B responds at the same address as the CSR, DRAM,
External Register Set, or any other slave on the PowerPC
bus.
rom_b_64 rom_b_64 indicates the type of ROM/FLASH
device/devices being used for Block B. When rom_b_64
is cleared, Block B consists of two 8-bit ROM/Flash
devices with one device connected to the upper Falcon
and the other device connected to the lower Falcon. When
rom_b_64 is set, Block B consists of either two 32-bit
devices or one 64-bit read-only device (such as a 64-bit
ROM SIMM). With two 32-bit devices, one device is
connected to the upper Falcon and the other device
connected to the lower Falcon. With one 64-bit device, the
device is controlled by either Falcon but connects to data
signals from both the upper and lower Falcons. rom_b_64
matches the inverse of the value that was on the CKD3 pin
at power-up reset. It cannot be changed by software.
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