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M29F800DT Datasheet(PDF) 33 Page - STMicroelectronics |
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M29F800DT Datasheet(HTML) 33 Page - STMicroelectronics |
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33 / 39 page  33/39 M29F800DT, M29F800DB APPENDIX C. BLOCK PROTECTION Block protection can be used to prevent any oper- ation 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 Program- mer technique, the In-System technique and Tem- porary Unprotection. Temporary Unprotection is controlled by the Reset/Block Temporary Unpro- tection pin, RP; this is described in the Signal De- scriptions section. 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 tech- niques for AMD parts will not work on STMicro- electronics parts. Care should be taken when changing drivers for one part to work on another. Programmer Technique The Programmer technique uses high (VID) volt- age 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 17, Programmer Equipment Block Protect Flowchart. To unprotect the whole chip it is necessary to pro- tect all of the blocks first, then all blocks can be un- protected at the same time. To unprotect the chip follow Figure 18, Programmer Equipment Chip Unprotect Flowchart. Table 27, Programmer Technique Bus Operations, 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. 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 micro- processor bus, therefore this technique is suitable for use after the Flash has been fitted to the sys- tem. To protect a block follow the flowchart in Figure 19, In-System 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 Fig- ure 20, In-System 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 pro- cedure before reaching the end. Chip Unprotect can take several seconds and a user message should be provided to show that the operation is progressing. Table 27. Programmer Technique Bus Operations, BYTE = VIH or VIL Operation E G W Address Inputs A0-A18 Data Inputs/Outputs DQ15A–1, DQ14-DQ0 Block Protect VIL VID VIL Pulse A9 = VID, A12-A18 Block Address Others = X X Chip Unprotect VID VID VIL Pulse A9 = VID, A12 = VIH, A15 = VIH Others = X X Block Protection Verify VIL VIL VIH A0 = VIL, A1 = VIH, A6 = VIL, A9=VID, A12-A18 Block Address Others = X Pass = XX01h Retry = XX00h Block Unprotection Verify VIL VIL VIH A0 = VIL, A1 = VIH, A6 = VIH, A9 = VID, A12-A18 Block Address Others = X Retry = XX01h Pass = XX00h |
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