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ADDRESSING UP TO 4 MBYTES OF EXTERNAL MEMORY

Figure 6. Static and Dynamic Segments

3.2 DEFINITION

STATIC SEGMENT (SS): A segment of memory which can always be accessed whatever the

value of the Dynamic Segment selected (value of Port 2 data register: P2DR). In an OTP/

ROM/FLASH microcontroller, the internal memory can always be accessed and therefore is

contained in static segments. For example in the ST90158, Segment 0 (ROM) and Seg 20

(RAM) are static segments

The size of the memory in a segment can be from zero to 64K. The number of static segments

and the amount of memory in each segment depends on the microcontroller.

In the case of ROMLESS devices, the static segment must be a special area of external

memory which is not connected to Port 2 and is therefore not dynamic.

At least one static segment is needed in any application.

DYNAMIC SEGMENT (DS): A segment of the external memory which is accessible only if it

has been selected by the user. Its access depends on the P2DR (Port 2 data register) value.

The size of a dynamic segment can be from 0 to 64K.

Dynamic segments

External memory

Static Segments

Internal or External

memory