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M29DW323DT70N6 Datasheet(PDF) 43 Page - STMicroelectronics |
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M29DW323DT70N6 Datasheet(HTML) 43 Page - STMicroelectronics |
43 / 49 page 43/49 M29DW323DT, M29DW323DB APPENDIX D. BLOCK PROTECTION Block protection can be used to prevent any oper- ation from modifying the data stored in the memo- ry. The blocks are protected in groups, refer to Appendix A, Tables 21 and 22 for details of the Protection Groups. Once protected, Program and Erase operations within the protected group 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. 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 group of blocks follow the flowchart in Figure 20, Programmer Equipment Block Protect Flowchart. To unprotect the whole chip it is neces- sary to protect all of the groups first, then all groups can be unprotected at the same time. To unprotect the chip follow Figure 21, Programmer Equipment Chip Unprotect Flowchart. Table 30, 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 memory has been fitted to the sys- tem. To protect a group of blocks follow the flowchart in Figure 22, In-System Block Protect Flowchart. To unprotect the whole chip it is necessary to protect all of the groups first, then all the groups can be unprotected at the same time. To unprotect the chip follow Figure 23, 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 30. Programmer Technique Bus Operations, BYTE = VIH or VIL Note: 1. Block Protection Groups are shown in Appendix A, Tables 21 and 22. Operation E G W Address Inputs A0-A20 Data Inputs/Outputs DQ15A–1, DQ14-DQ0 Block (Group) Protect(1) VIL VID VIL Pulse A9 = VID, A12-A20 Block Address Others = X X Chip Unprotect VID VID VIL Pulse A9 = VID, A12 = VIH, A15 = VIH Others = X X Block (Group) Protection Verify VIL VIL VIH A0 = VIL, A1 = VIH, A6 = VIL, A9=VID, A12-A20 Block Address Others = X Pass = XX01h Retry = XX00h Block (Group) Unprotection Verify VIL VIL VIH A0 = VIL, A1 = VIH, A6 = VIH, A9 = VID, A12-A20 Block Address Others = X Retry = XX01h Pass = XX00h |
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