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Rabbit 4000 Microprocessor User’s Manual
Either of the two most significant address bits (which are used to select the quadrant) can
be inverted, providing the ability to bank-switch other pages from a larger memory device
into the same memory bank.
Code is executed in the 64KB logical memory space, which is divided into four segments:
root, data, stack, and XMEM. The root segment is mapped directly to physical address
0x000000, while the data and stack segments can be mapped to 4KB boundaries anywhere
in the physical space. The boundaries between the root and data segments and the data and
stack segments can be adjusted in 4KB blocks as well.
The XMEM segment is a fixed 8KB and points to a physical memory address specified in
the XPC register. It is possible to run code in the XMEM window, providing an easy
means of storing and executing code beyond the 64KB logical memory space. Special call
and return instructions to physical addresses are provided that automatically update the
XPC register as necessary.
Figure 5-2. Logical and Physical Memory Mapping
64KB
16MB
LOGICAL
ADDRESS MAP
PHYSICAL
ADDRESS MAP
DATA
SEGMENT
STACK
SEGMENT
000000
FFFFFF
0000
FFFF
E000
x
000
y
000
SEGSIZE
REGISTER
(0x13) R/W
7 4 3 0
y
x
XMEM
SEGMENT
ROOT
SEGMENT
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