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X24645PM Datasheet(PDF) 9 Page - Xicor Inc. |
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X24645PM Datasheet(HTML) 9 Page - Xicor Inc. |
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9 / 18 page  X24645 9 WRITE PROTECT REGISTER The Write Protect Register (WPR) is located at the highest address, 1FFFh. Figure 11. Write Protect Register WPR.1 = WEL – “Write Enable” Latch (Volatile) 0 = Write enable latch reset, writes disabled 1 = Write enable latch set, writes enabled If WEL = “0” then “no ACK” after first byte of input data. WPR.2 = RWEL – “Register Write Enable” Latch (Volatile) 0 = Register write enable latch reset, writes dis- abled 1 = Register write enable latch set, writes enabled WPR.3, WPR.4 = BP0, BP1 – Block Protect Bits (Nonvolatile) (See Block Protect section for definition) WPR.7 = WPEN – Write Protect Enable Bit (Nonvolatile) (See Hardware Write Protect section for definition) Writing to the Write Protect Register The Write Protect Register is written by performing a random write of one byte directly to address, 1FFFh. If a page write is performed starting with any address other than 1FFF, the byte in the array at address 1FFFh will be written instead of the Write Protect Register (assuming writes are not disabled by the block protect register). The state of the Write Protect Register can be read by performing a random read at address 1FFFh at any time. If a sequential read starting at any other address than 1FFFh is performed, the contents of the byte in the array at 1FFFh is read out instead of the Write Protect Register. 7 6 5 4 3 2 1 0 WPEN 0 0 BP1 BP0 RWEL WEL 0 2783 ILL F15.1 WPR (ADDR = 1FFFh) WEL and RWEL are volatile latches that power-up in the LOW (disabled) state. A write to any address other than 1FFFh, where the Write Protect Register is located, will be ignored (no ack) until the WEL bit is set HIGH. The WEL bit is set by writing 0000001x to address 1FFFh. Once set, WEL remains HIGH until either reset (by writing 00000000 to 1FFFh) or until the part powers-up again. The RWEL bit controls writes to the block protect bits. RWEL is set by first setting WEL to “1” and then writing 0000011x to address 1FFFh. RWEL must be set in order to change the block protect bits, BP0 and BP1, or the WPEN bit. RWEL is reset when the block protect or WPEN bits are changed, or when the part powers-up again. Programming the BP or WPEN Bits A three step sequence is required to change the nonvolatile Block Protect or Write Protect Enable: 1) Set WEL = 1 (write 00000010 to address 1FFFh, volatile write cycle) (Start) 2) Set RWEL = 1 (write 00000110 to address 1FFFh, volatile write cycle) (Start) 3) Set BP1, BP0, and/or WPEN bits (Write w00yz010 to address 1FFFh) w = WPEN, y = BP1, Z = BP0, (Stop) Step 3 is a nonvolatile write cycle, requiring 10ms to complete. RWEL is reset to “0” by this write cycle, requiring another write cycle to set RWEL again before the block protect bits can be changed. RWEL must be “0” in step 3; if w00yz110 is written to address 1FFFh, RWEL is set but WPEN, BP1 and BP0 are not changed (the device remains at step 2). |
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