Atmel AT85DVK-07 Spezifikationen PDF herunterladen (Seite 180)

180

AT85C51SND3Bx

7632A–MP3–03/06

Write Protection The NFC provides a hardware mechanism to protect full or part of the memory against

any spurious writing. This is achieved by using the

NFWP signal and connecting it to the

WP pins of the memories.

The NFWP signal is automatically asserted in the following conditions:

• The internal voltage is out of specified value (brown-out detection)

• An external reset has been applied to the device

• A watchdog reset has been triggered (bad code execution)

• A write or erase to the protected area has been triggered (bad code execution)

User Whole Memory Protection The user has the possibility to protect all the flash devices (NF and SMC) by asserting

the external

NFWP signal. This is achieved by setting the NFWP bit in NFCON. All the

memories are protected at the same time, i.e. NF and SMC if a SMC is present.

Hardware Protected Area A user defined area in the memories (a certain amount of blocks) can be locked against

writing or erasing. This is done by giving to the controller the first protected block (FPB)

address, the last protected block address (LPB) and the device number to be locked

(PDEV). All this information is part of the Configuration Descriptor.

Table 198 summa-

rizes which device is locked or not.

The protected area is practically used for user firmwares, codec firmwares, fonts and

other configuration data.

Table 198. Protected Device versus PDEV Value

Then, if a device is protected, the following policy is applied:

• If FPB is lower than LPB, the protected area is a contiguous area starting from FPB

to LPB.

• If FPB is higher than LPB, there are two protected areas: any block address that is

below LPB and any block address that is above FPB.

• If FPB is equal to LPB, all the flash is protected.This is the default behavior.

PDEV3 PDEV2 PDEV1 PDEV0 Description

0 0 0 0 No locked devices

x x x 1 The blocks [FPB; LPB] of NF device 0 are locked

x x 1 x The blocks [FPB; LPB] of NF device 1 are locked

x 1 x x The blocks [FPB; LPB] of NF device 2 are locked

1 x x x

The blocks [FPB; LPB] of NF device 3 (SMCEN=0) or of SMC

(SMCEN=1) are locked

1 2 ... 175 176 177 178 179 180 181 182 183 184 185 ... 262 263

Keine Kommentare

Atmel AT85DVK-07 Spezifikationen Seite 180