7/14

ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY

Using the ST90158, the maximum accessible memory will be:

4M (total accessible memory)

- 4 x 64 k (internal segments)

+ 1K (internal RAM)

+ 64K (internal ROM)

________________________

= 3905K bytes

The size of each dynamic segment is 64 Kbytes in this case. We can represent the memory

seen by the microcontroller as shown in Figure 8..

Note: When using ST92F120, it is not possible to access any external segments other than

segments 2 and 3. So the maximum amount of external memory that can be accessed by the

ST92F120 is 128 Kbytes.

Figure 8. Memory map for accessing 4M of external memory with the ST90158

Seg 0

Seg 1

Seg 21

Seg 3F

64K Internal ROM

Seg 22

Seg 20

1K RAM

Reserved

Reserved

64K External Memory

Seg 23

64K External Memory

Seg 1F

64K External Memory

64K External Memory

Dynamic segment

Static segment