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M28C16-250MS1T Datasheet(PDF) 5 Page - STMicroelectronics |
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M28C16-250MS1T Datasheet(HTML) 5 Page - STMicroelectronics |
5 / 17 page Software Data Protection The M28LV16 offers a software controlled write protection facility that allows the user to inhibit all write modes to the device including the Chip Erase instruction. This can be useful in protecting the memory from inadvertent write cycles that may occur due to uncontrolled bus conditions. The M28LV16 is shipped as standard in the ”unpro- tected” state meaning that the memory contents can be changed as required by the user. After the Software Data Protection enable algorithm is is- sued, the device enters the ”Protect Mode” of operation where no further write commands have any effect on the memory contents. The device remains in this mode until a valid Software Data Protection (SDP) disable sequence is received whereby the device reverts to its ”unprotected” state. The Software Data Protection is fully non- volatile and is not changed by power on/off se- quences. To enable the Software Data Protection (SDP) the device requires the user to write (with a Page Write) three specific data bytes to three specific memory locations as per Figure 5. Similarly to disable the Software Data Protection the user has to write specific data bytes into six different locations as per Figure 6 (with a Page Write). This complex series ensures that the user will never enable or disable the Software Data Protection accidentally. AI01509B WRITE AAh in Address 555h WRITE 55h in Address 2AAh WRITE A0h in Address 555h SDP is set WRITE AAh in Address 555h WRITE 55h in Address 2AAh WRITE A0h in Address 555h Write Page (1 up to 64 bytes) WRITE IN MEMORY WHEN SDP IS SET SDP ENABLE ALGORITHM Page Write Instruction (Note 1) Page Write Instruction (Note 1) WRITE is enabled Figure 5. Software Data Protection Enable Algorithm and Memory Write AI01510 WRITE AAh in Address 555h WRITE 55h in Address 2AAh WRITE 80h in Address 555h Unprotected State WRITE AAh in Address 555h WRITE 55h in Address 2AAh WRITE 20h in Address 555h Page Write Instruction Figure 6. Software Data Protection Disable Algorithm Note: 1. MSB Address bits (A6 to A10) differ during these specific Page Write operations. 5/17 M28LV16 |
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