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AT89C51ED2-RDTIM 数据表(PDF) 105 Page - ATMEL Corporation |
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AT89C51ED2-RDTIM 数据表(HTML) 105 Page - ATMEL Corporation |
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105 / 137 page  105 AT89C51RD2/ED2 4235E–8051–04/04 Functional Description Software Security Bits (SSB) The SSB protects any Flash access from ISP command. The command "Program Software Security Bit" can only write a higher priority level. There are three levels of security: • level 0: NO_SECURITY (FFh) This is the default level. From level 0, one can write level 1 or level 2. • level 1: WRITE_SECURITY (FEh) For this level it is impossible to write in the Flash memory, BSB and SBV. The Bootloader returns ’P’ on write access. From level 1, one can write only level 2. • level 2: RD_WR_SECURITY (FCh The level 2 forbids all read and write accesses to/from the Flash/EEPROM memory. The Bootloader returns ’L’ on read or write access. Only a full chip erase in parallel mode (using a programmer) or ISP command can reset the software security bits. From level 2, one cannot read and write anything. Table 73. Software Security Byte Behavior Level 0 Level 1 Level 2 Flash/EEPROM Any access allowed Read-only access allowed Any access not allowed Fuse Bit Any access allowed Read-only access allowed Any access not allowed BSB & SBV Any access allowed Read-only access allowed Any access not allowed SSB Any access allowed Write level 2 allowed Read-only access allowed Manufacturer Info Read-only access allowed Read-only access allowed Read-only access allowed Bootloader Info Read-only access allowed Read-only access allowed Read-only access allowed Erase Block Allowed Not allowed Not allowed Full Chip Erase Allowed Allowed Allowed Blank Check Allowed Allowed Allowed |
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