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M29W400T-90N5TR Datasheet(PDF) 9 Page - STMicroelectronics |
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M29W400T-90N5TR Datasheet(HTML) 9 Page - STMicroelectronics |
9 / 34 page Block Protection. Each block can be separately protected against Program or Erase on program- ming equipment. Block protection provides addi- tional data security, as it disables all program or erase operations.This mode is activatedwhen both A9 and G are raised to VID and an address in the block is applied on A12-A17. The Block Protection algorithm is shown in Figure 14. Block protectionis initiated on the edge of W falling to VIL. Then after a delay of 100 µs, the edge of W rising to VIH ends the protection operations. Block protection verify is achieved by bringing G, E, A0 and A6 to VIL and A1 to VIH, while W is at VIH and A9 at VID. Under these conditions, reading the data output will yield 01h if the block defined by the inputs on A12-A17 is protected. Any attempt to program or erase a pro- tected block will be ignored by the device. Block Temporary Unprotection. Any previously protected block can be temporarily unprotected in order to change stored data. The temporary unpro- tection mode is activated by bringing RP to VID. During the temporary unprotection mode the pre- viously protected blocks are unprotected. A block can be selected and data can be modified by executing the Erase or Program instruction with the RP signal held at VID. When RP is returned to VIH, all the previously protected blocks are again pro- tected. Block Unprotection. All protected blocks can be unprotected on programming equipment to allow updating of bit contents. All blocks must first be protected before the unprotectionoperation. Block unprotection is activated when A9, G and E are at VID and A12, A15 at VIH. The Block Unprotection algorithm is shown in Figure 15. Unprotection is initiated by the edge of W falling to VIL. After a delay of 10ms, the unprotection operation will end. Un- protection verify is achieved by bringing G and E to VIL while A0 is at VIL, A6 and A1 are at VIH and A9 remains at VID. In these conditions, reading the output data will yield 00h if the block defined by the inputs A12-A17 has been succesfully unprotected. Each block must be separatelyverified by giving its address in order to ensure that it has been unpro- tected. INSTRUCTIONS AND COMMANDS The Command Interface latches commands writ- ten to the memory. Instructions are made up from one or more commands to perform Read Memory Array, Read Electronic Signature, Read Block Pro- tection, Program, Block Erase, Chip Erase, Erase Suspend and Erase Resume. Commands are made of address and data sequences. The in- structions require from 1 to 6 cycles, the first or first three of which are always write operations used to initiate the instruction. They are followed by either further write cycles to confirm the first command or execute the command immediately. Command se- quencing must be followed exactly. Any invalid combination of commands will reset the device to Read Array. The increased number of cycles has been chosen to assure maximum data security. Instructions are initialised by two initial Coded cy- cles which unlock the Command Interface. In addi- tion, for Erase, instruction confirmation is again preceded by the two Coded cycles. Hex Code Command 00h Invalid/Reserved 10h Chip Erase Confirm 20h Reserved 30h Block Erase Resume/Confirm 80h Set-up Erase 90h Read Electronic Signature/ Block Protection Status A0h Program B0h Erase Suspend F0h Read Array/Reset Table 7. Commands 9/34 M29W400T, M29W400B |
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