Filter
Top Products
25
1745D–ATARM–04-Nov-05
AT91M55800A
11.1 External Memory Mapping
The memory map associates the internal 32-bit address space with the external 24-bit
address bus.
The memory map is defined by programming the base address and page size of the external
memories (see EBI User Interface registers EBI_CSR0 to EBI_CSR7). Note that A0 - A23 is
only significant for 8-bit memory; A1 - A23 is used for 16-bit memory.
If the physical memory device is smaller than the programmed page size, it wraps around and
appears to be repeated within the page. The EBI correctly handles any valid access to the
memory device within the page. (See Figure 11-1.)
In the event of an access request to an address outside any programmed page, an Abort sig-
nal is generated. Two types of Abort are possible: instruction prefetch abort and data abort.
The corresponding exception vector addresses are respectively 0x0000 000C and 0x0000
0010. It is up to the system programmer to program the error handling routine to use in case of
an Abort (see the ARM7TDMI datasheet for further information).
Figure 11-1. External Memory Smaller than Page Size
1-Mbyte Device
1-Mbyte Device
1-Mbyte Device
1-Mbyte Device
Memory
Map
Hi
Low
Hi
Low
Hi
Low
Hi
Low
Base
Base + 1M Byte
Base + 2M Byte
Base + 3M Byte
Base + 4M Byte
Repeat 1
Repeat 2
Repeat 3