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M29W640FT Datasheet(PDF) 64 Page - Numonyx B.V |
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M29W640FT Datasheet(HTML) 64 Page - Numonyx B.V |
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64 / 71 page  Block protection M29W640FT, M29W640FB 64/71 Appendix D Block protection Block protection can be used to prevent any operation from modifying the data stored in the memory. The blocks are protected in groups, refer to Appendix A: Block addresses, Table 21 and Table 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 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 Signal Descriptions section. D.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 group of blocks follow the flowchart in Figure 16: Programmer Equipment Group Protect flowchart. To unprotect the whole chip it is necessary to protect all of the groups first, then all groups can be unprotected at the same time. To unprotect the chip follow Figure 17: Programmer Equipment Chip Unprotect flowchart. Table 30: 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. D.2 In-System technique The In-System technique requires a high voltage level on the Reset/Blocks Temporary Unprotect pin, RP(1). 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 memory has been fitted to the system. To protect a group of blocks follow the flowchart in Figure 18: In-System Equipment Group 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 19: 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. Note: RP can be either at VIH or at VID when using the In-System Technique to protect the Extended Block. |
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