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M29W800DT Datasheet(PDF) 45 Page - Numonyx B.V |
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M29W800DT Datasheet(HTML) 45 Page - Numonyx B.V |
45 / 52 page M29W800DT, M29W800DB Block protection 45/52 Appendix C Block protection Block protection can be used to prevent any operation from modifying the data stored in the Flash. Each block can be protected individually. Once protected, program and erase operations on the block fail to change the data. There are three techniques that can be used to control block protection, these are the programmer technique, the in-system technique and temporary unprotection. Temporary unprotection is controlled by the reset/block temporary unprotection pin, RP; this is described in the Section 2: Signal descriptions. Unlike the command interface of the program/erase controller, the techniques for protecting and unprotecting blocks change between different Flash memory suppliers. For example, the techniques for AMD parts will not work on Numonyx parts. Care should be taken when changing drivers for one part to work on another. C.1 Programmer technique The programmer technique uses high (VID) voltage levels on some of the bus pins. These cannot be achieved using a standard microprocessor bus, therefore the technique is recommended only for use in programming equipment. To protect a block follow the flowchart in Figure 18: Programmer equipment block protect flowchart. To unprotect the whole chip it is necessary to protect all of the blocks first, then all blocks can be unprotected at the same time. To unprotect the chip follow Figure 19: Programmer equipment chip unprotect flowchart. Table 28: Programmer technique bus operations, BYTE = VIH or VIL, gives a summary of each operation. The timing on these flowcharts is critical. Care should be taken to ensure that, where a pause is specified, it is followed as closely as possible. Do not abort the procedure before reaching the end. Chip unprotect can take several seconds and a user message should be provided to show that the operation is progressing. C.2 In-system technique The in-system technique requires a high voltage level on the reset/blocks temporary unprotect pin, RP. This can be achieved without violating the maximum ratings of the components on the microprocessor bus, therefore this technique is suitable for use after the Flash has been fitted to the system. To protect a block follow the flowchart in Figure 20: In-system equipment block protect flowchart. To unprotect the whole chip it is necessary to protect all of the blocks first, then all the blocks can be unprotected at the same time. To unprotect the chip follow Figure 21: In- system equipment chip unprotect flowchart. The timing on these flowcharts is critical. Care should be taken to ensure that, where a pause is specified, it is followed as closely as possible. Do not allow the microprocessor to service interrupts that will upset the timing and do not abort the procedure before reaching the end. Chip unprotect can take several seconds and a user message should be provided to show that the operation is progressing. |
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