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M9346-BN3T Datasheet(PDF) 14 Page - STMicroelectronics |
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M9346-BN3T Datasheet(HTML) 14 Page - STMicroelectronics |
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14 / 34 page  M93S66, M93S56, M93S46 14/34 WRITE PROTECTION AND THE PROTECTION REGISTER The Protection Register on the M93Sx6 is used to adjust the amount of memory that is to be write protected. The write protected area extends from the address given in the Protection Register, up to the top address in the M93Sx6 device. Two flag bits are used to indicate the Protection Register status: – Protection Flag: this is used to enable/disable protection of the write-protected area of the M93Sx6 memory – OTP bit: when set, this disables access to the Protection Register, and thus prevents any further modifications to the value in the Protection Register. The lower-bound memory address is written to the Protection Register using the Protection Register Write (PRWRITE) instruction. It can be read using the Protection Register Read (PRREAD) instruc- tion. The Protection Register Enable (PREN) instruc- tion must be executed before any PRCLEAR, PRWRITE or PRDS instruction, and with appropri- ate levels applied to the Protection Enable (PRE) and Write Enable (W) signals. Write-access to the Protection Register is achieved by executing the following sequence: – Execute the Write Enable (WEN) instruction – Execute the Protection Register Enable (PREN) instruction – Execute one PRWRITE, PRCLEAR or PRDS instructions, to set a new boundary address in the Protection Register, to clear the protection address (to all 1s), or permanently to freeze the value held in the Protection Register. Protection Register Read The Protection Register Read (PRREAD) instruc- tion outputs, on Serial Data Output (Q), the con- tent of the Protection Register, followed by the Protection Flag bit. The Protection Enable (PRE) signal must be driven High before and during the instruction. As with the Read Data from Memory (READ) in- struction, a dummy 0 bit is output first. Since it is not possible to distinguish between the Protection Register being cleared (all 1s) or having been writ- ten with all 1s, the user must check the Protection Flag status (and not the Protection Register con- tent) to ascertain the setting of the memory protec- tion. Protection Register Enable The Protection Register Enable (PREN) instruc- tion is used to authorize the use of instructions that modify the Protection Register (PRWRITE, PRCLEAR, PRDS). The Protection Register En- able (PREN) instruction does not modify the Pro- tection Flag bit value. Note: A Write Enable (WEN) instruction must be executed before the Protection Register Enable (PREN) instruction. Both the Protection Enable (PRE) and Write Enable (W) signals must be driv- en High during the instruction execution. Protection Register Clear The Protection Register Clear (PRCLEAR) in- struction clears the address stored in the Protec- tion Register to all 1s, so that none of the memory is write-protected by the Protection Register. How- ever, it should be noted that all the memory re- mains protected, in the normal way, using the Write Enable (WEN) and Write Disable (WDS) in- structions. The Protection Register Clear (PRCLEAR) in- struction clears the Protection Flag to 1. Both the Protection Enable (PRE) and Write Enable (W) signals must be driven High during the instruction execution. Note: A Protection Register Enable (PREN) in- struction must immediately precede the Protection Register Clear (PRCLEAR) instruction. Protection Register Write The Protection Register Write (PRWRITE) instruc- tion is used to write an address into the Protection Register. This is the address of the first word to be protected. After the Protection Register Write (PRWRITE) instruction has been executed, all memory locations equal to and above the speci- fied address are protected from writing. The Protection Flag bit is set to 0, and can be read with Protection Register Read (PRREAD) instruc- tion. Both the Protection Enable (PRE) and Write Enable (W) signals must be driven High during the instruction execution. Note: A Protection Register Enable (PREN) in- struction must immediately precede the Protection Register Write (PRWRITE) instruction, but it is not necessary to execute first a Protection Register Clear (PRCLEAR). Protection Register Disable The Protection Register Disable (PRDS) instruc- tion sets the One Time Programmable (OTP) bit. This instruction is a ONE TIME ONLY instruction which latches the Protection Register content, this content is therefore unalterable in the future. Both the Protection Enable (PRE) and Write Enable (W) signals must be driven High during the instruction execution. The OTP bit cannot be directly read, it can be checked by reading the content of the Pro- tection Register, using the Protection Register Read (PRREAD) instruction, then by writing this same value back into the Protection Register, us- |
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