at85c51snd3 ATMEL Corporation, at85c51snd3 Datasheet - Page 181

• Manufacturer Part Number: at85c51snd3
• Description: At85c51snd3 Single-chip Digital Audio Decoder - Encoder With Usb 2.0 Interface
• Manufacturer: ATMEL Corporation

Write Protection
User Whole Memory Protection
Hardware Protected Area
7632D–MP3–01/07
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 user has the possibility to protect all the flash devices (NF and SMC) by asserting
the external NFWP signal. This is achieved by clearing the NFWP bit in NFCON. All the
memories are protected at the same time, i.e. NF and SMC if a SMC is present.
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 199 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 199. Protected Device versus PDEV Value
Then, if a device is protected, the following policy is applied:
•
•
•
PDEV3 PDEV2 PDEV1 PDEV0 Description
0
1
x
x
x
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)
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.
0
x
x
1
x
0
x
1
x
x
0
1
x
x
x
No locked devices
The blocks [FPB; LPB] of NF device 0 are locked
The blocks [FPB; LPB] of NF device 1 are locked
The blocks [FPB; LPB] of NF device 2 are locked
The blocks [FPB; LPB] of NF device 3 (SMCEN=0) or of SMC
(SMCEN=1) are locked
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