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M28W160ECT85N1T Datasheet(PDF) 16 Page - Numonyx B.V |
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M28W160ECT85N1T Datasheet(HTML) 16 Page - Numonyx B.V |
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16 / 50 page  M28W160ECT, M28W160ECB 16/50 BLOCK LOCKING The M28W160EC features an instant, individual block locking scheme that allows any block to be locked or unlocked with no latency. This locking scheme has three levels of protection. ■ Lock/Unlock - this first level allows software- only control of block locking. ■ Lock-Down - this second level requires hardware interaction before locking can be changed. ■ VPP ≤VPPLK - the third level offers a complete hardware protection against program and erase on all blocks. The lock status of each block can be set to Locked, Unlocked, and Lock-Down. Table 9., de- fines all of the possible protection states (WP, DQ1, DQ0), and APPENDIX C., Figure 22., shows a flowchart for the locking operations. Reading a Block’s Lock Status The lock status of every block can be read in the Read Electronic Signature mode of the device. To enter this mode write 90h to the device. Subse- quent reads at the address specified in Table 5., will output the lock status of that block. The lock status is represented by DQ0 and DQ1. DQ0 indi- cates the Block Lock/Unlock status and is set by the Lock command and cleared by the Unlock command. It is also automatically set when enter- ing Lock-Down. DQ1 indicates the Lock-Down sta- tus and is set by the Lock-Down command. It cannot be cleared by software, only by a hardware reset or power-down. The following sections explain the operation of the locking system. Locked State The default status of all blocks on power-up or af- ter a hardware reset is Locked (states (0,0,1) or (1,0,1)). Locked blocks are fully protected from any program or erase. Any program or erase oper- ations attempted on a locked block will return an error in the Status Register. The Status of a Locked block can be changed to Unlocked or Lock-Down using the appropriate software com- mands. An Unlocked block can be Locked by issu- ing the Lock command. Unlocked State Unlocked blocks (states (0,0,0), (1,0,0) (1,1,0)), can be programmed or erased. All unlocked blocks return to the Locked state after a hardware reset or when the device is powered-down. The status of an unlocked block can be changed to Locked or Locked-Down using the appropriate software commands. A locked block can be un- locked by issuing the Unlock command. Lock-Down State Blocks that are Locked-Down (state (0,1,x))are protected from program and erase operations (as for Locked blocks) but their lock status cannot be changed using software commands alone. A Locked or Unlocked block can be Locked-Down by issuing the Lock-Down command. Locked-Down blocks revert to the Locked state when the device is reset or powered-down. The Lock-Down function is dependent on the WP input pin. When WP=0 (VIL), the blocks in the Lock-Down state (0,1,x) are protected from pro- gram, erase and protection status changes. When WP=1 (VIH) the Lock-Down function is disabled (1,1,1) and Locked-Down blocks can be individu- ally unlocked to the (1,1,0) state by issuing the software command, where they can be erased and programmed. These blocks can then be locked again (1,1,1) and unlocked (1,1,0) as desired while WP remains high. When WP is low, blocks that were previously Locked-Down return to the Lock- Down state (0,1,x) regardless of any changes made while WP was high. Device reset or power- down resets all blocks, including those in Lock- Down, to the Locked state. Locking Operations During Erase Suspend Changes to block lock status can be performed during an erase suspend by using the standard locking command sequences to unlock, lock or lock-down a block. This is useful in the case when another block needs to be updated while an erase operation is in progress. To change block locking during an erase opera- tion, first write the Erase Suspend command, then check the status register until it indicates that the erase operation has been suspended. Next write the desired Lock command sequence to a block and the protection status will be changed. After completing any desired lock, read, or program op- erations, resume the erase operation with the Erase Resume command. If a block is locked or locked-down during an erase suspend of the same block, the locking status bits will be changed immediately, but when the erase is resumed, the erase operation will complete. Locking operations cannot be performed during a program suspend. Refer to APPENDIX D., COMMAND INTERFACE AND PROGRAM/ ERASE CONTROLLER STATE, for detailed infor- mation on which commands are valid during erase suspend. |
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