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5. M
EMORY
M
ANAGEMENT
5.1 Overview
The Rabbit 4000 supports both 8-bit and 16-bit external flash and SRAM devices; three
chip selects and two read/write-enable strobes allow up to six external devices to be
attached at once. The 8-bit mode allows 0, 1, 2, or 4 wait states to be specified for each
device, and the 16-bit mode allows 0 to 9 wait states depending on the settings. Both 8-bit
and 16-bit page-mode devices are also supported.
The Rabbit 4000’s physical memory space contains four consecutive banks, each of which
can be mapped to an individual chip-select/enable strobe pair. The banks can be set for
equal sizes ranging from 128KB up to 4MB, providing a total physical memory range from
512KB up to 16MB. Figure 5-1 shows a sample configuration.
Figure 5-1. Mapping Rabbit 4000 Physical Memory Space
1MB
0x00000
0x40000
0x3FFFF
0x80000
0x7FFFF
0xC0000
0xBFFFF
0xFFFFF
Memory Bank 3
MB3CR = 0x86
Memory Bank 2
MB2CR = 0xC5
Memory Bank 1
MB1CR = 0xC0
Memory Bank 0
MB0CR = 0xC0
1 wait state
/CS2
/OE1
/WE1
0 wait states
/CS1
/OE1
/WE1
0 wait states
/CS0
/OE0
/WE0
512KB
Flash
256KB
SRAM
256KB
SRAM
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