User`s manual

30 rabbit.com Rabbit Memory Organization

Separate I&D logical addresses map to physical addresses by inverting address lines A16, the most signifi-

cant address bit or both.The most significant address bit may be A18-A23, depending on the MECR set-

ting. The MMU Instruction/Data Register (MMIDR) determines which lines are inverted. Please see the

Rabbit 4000 Microprocessor User’s Manual for more information about the MMIDR.

The following diagram (Figure 5-3) shows the physical address space when separate I&D space is

enabled, SEGSIZE = 0xD3 and code is compiled to flash.

The inversion of A16 causes the root constants in the data space to be addressed in the second 64 KB block

of the flash. The inversion of MSB (A19 in this example) causes the root data in the data space to be

located in RAM (RAM is mapped at 0x80000), starting at 0x83000 as directed by the lower nibble of

SEGSIZE.

Figure 5-3 Physical Address Space when Separate I&D Space is Enabled

and the Quadrant Size is 256 KB

512K RAM

512K Flash

0x00000

0x0D000

0x10000

0x13000

52K

Root Constants

Root Data

0x80000

44K

0x83000

0x8D000

0xC0000

Invert

A16

Invert

A19

Root Code

0xFFFFF

0x7FFFF