Rabbit 2000, User Manual

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User’s Manual 93
8.2 Memory Interface Unit
The 20-bit memory addresses generated by the memory-mapping unit feed into the mem-
ory interface unit. The memory interface unit has a separate write-only control register
(see Table 8-3) for each 256K quadrant of the 1M physical memory. This control register
specifies how memory access requests to that quadrant are to be dispatched to the memory
chips connected to the Rabbit. There are three separate chip select output lines (/CS0,
/CS1, and /CS2) that can be used to select one of three different memory chips. A field in
the control register determines which chip select is selected for memory accesses to the
quadrant. The same chip select line may be accessed in more than one quadrant. For
example, if a 512K RAM is installed and is selected by /CS1, it would be appropriate to
use /CS1 for accesses to the 3rd and 4th quadrants, thus mapping the RAM chip to
addresses 0x80000 to 0x0FFFFF.