AT697F datasheet(30/155 Pages) ATMEL

30 / 155 page

7703C–AERO–6/09

AT697F ADVANCE INFORMATION

Write Protection

Two write protection schemes are provided to prevent accidental over-writing to the RAM area,

the “Start/End address Scheme” and the “Mask Scheme”. These two schemes are explained in

the following two sub-chapter

Start/End address

Scheme

Two memory areas are defined by using a start-address and an end-address register. The first

address of the protected memory area is calculated as 0x40000000 + START*4. The last

address of the protected memory area is calculated as 0x40000000 + END*4.

Table 12.

START

Start Address Register (WPSTAx)

Table 13.

STOP

US SU

End Address Register (WPSTOx)

Setting WPSTAx BPx to logical one, any access inside the two areas defined by the start/end

registers will cause a memory exception (trap 0x2B). The first address of the protected against

write operation is calculated as 0x40000000 + START*4. The first address outside the protected

memory area is calculated as 0x40000000 + END*4 + 4.

Setting WPSTAx BPx to logical zero the area between the start address and the end address

defines the memory where write access is permitted, and a write access outside both areas will

cause a memory exception (trap 0x2B). The first address where write operation is permitted is

calculated as 0x40000000 + START*4. The first address outside the protected allowed area is

calculated as 0x40000000 + END*4 + 4.

The start/end address protection scheme is enabled when at least one of the user mode protec-

tion and the supervisor mode protection is valid. The write protection can be configured to

prevent the application from user and/or supervisor write access.

•

Memory is protected against User write when WPSTOx USx bit is set logical 1

•

Memory is protected against Superviser write when WPSTOx SUx bit is set logical 1

AT697F Datasheet(PDF) 30 Page - ATMEL Corporation