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Rabbit 5000 Microprocessor User’s Manual
Figure 5-3. MMU Operation
5.3.2 Memory Bank Operation
On startup the Rabbit 5000 checks the status of the SYSCFG pins. To provide support for
external memory, both SYSCFG pins should be set low and Memory Bank 0 enabled to
use /CS0, /OE0, and /WE0 in 8-bit mode with four wait states and write protection
enabled. It is expected that an external flash device containing startup code is attached to
those strobes. The other memory banks come up undefined and their controls should be set
via the appropriate MBxCR register to a valid setting before use.
If SYSCFG0 is high and SYSCFG1 is low, Memory Bank 0 is enabled to use /CS3, /OE0,
and /WE0 in 16-bit mode. This allows the processor to start operation directly out of the
internal SRAM.
The size of the memory banks is defined in the MECR register. The default size is 256 KB
(the bank selection looks at the two most significant address bits), but this value can be
adjusted down to 128 KB or up to 4 MB per bank.
0
DATASEG
16-bit logical address
20-bit physical address
0
+
16-bit logical address
+
DATASEGL
DATASEGH
16-bit logical address
+
0
16-bit logical address
20-bit physical address
0
+
STKSEG
STKSEGL
24-bit physical address
24-bit physical address
STKSEGH
16-bit logical address
+
24-bit physical address
0
16-bit logical address
20-bit physical address
0
+
XPC
LXPC
Содержание Rabbit 5000
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