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ML671000 User’s Manual
Chapter 12
External Memory Controller (XMC)
12-7
12.1.4. Address Space
Although the CPU architecture theoretically provides a 32-bit address space of 4 gigabytes, this LSI
ignores the top six bits (A31 to A26) and uses 26-bit addressing to access only the first 64
megabytes.
Table 12-3 outlines the memory types for the regions in these four 16-megabyte banks.
Table 12-3
Address Space Regions
Bank
Addresses
Assignment
Size
Chip
Select
Data
Bus
Width
0x00000000 to 0x001FFFFF
External ROM, RAM,
and peripherals
2MB
nCS0
8/16
0x00200000 to 0x003FFFFF
Internal RAM
2MB
-
32
0x00400000 to 0x005FFFFF
Core bus I/O space
2MB
-
32
0x00600000 to 0x006FFFFF
Peripheral bus I/O space
1MB
-
16
0x00700000 to 0x007FFFFF
Internal reserved region
1MB
-
16
0
0x00800000 to 0x00FFFFFF
External ROM, RAM,
and peripherals
8MB
nCS0
8/16
1
0x01000000 to 0x01FFFFFF
External ROM, RAM,
and peripherals
16MB
nCS1
8/16
2
0x02000000 to 0x02FFFFFF
External DRAM
16MB
nRAS0
8/16
3
0x03000000 to 0x03FFFFFF
External DRAM
16MB
nRAS1
8/16
The 64-megabyte address space is divided into four 16-megabyte banks specified by the top two
address bits (A25 and A24).
Each bank is assigned a specific type and provides the appropriate strobe signals to enable the direct
connection of memory and peripheral devices of that type.
Bank 0 is further divided in the following regions.
0x00000000 to 0x001FFFFF External memory (ROM, RAM, and peripherals)
0x00200000 to 0x003FFFFF Internal RAM. Only 4 kilobytes (0x00200000 to 0x00200FFF) is
physically present.
0x00400000 to 0x005FFFFF Core bus I/O space. This contains the CPU control block control
registers.
0x00600000 to 0x006FFFFF Peripheral bus I/O space. This contains the control registers for all on-
chip peripherals outside the CPU control block.
0x00700000 to 0x007FFFFF Reserved space not available for use.
0x00800000 to 0x00FFFFFF External memory (ROM, RAM, and peripherals)
Do not access bank 0 addresses between 0x00200000 to 0x006FFFFF that do not have internal RAM
or a control register physically present. Operation is not guaranteed.
Bank 1 is accessed as an external memory space for ROM, RAM, and I/O; banks 2 and 3, as external
DRAM spaces.
Bank 2 or 3 access uses the output signals nRAS, nCAS, and a multiplexed address.
Each bank has its own bus width setting (8 or 16 bits).
Figure 12-2 shows the address space.