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11 / 17 page Write Protection. Data in the upper four blocks of 256 bytes of the memory may be write protected. The memory is write protected between a boundary address and the top of memory (address 7FFh).The boundary address is user defined by writing it in the Block Address Pointer (location 7FFh). The Block Address Pointer is an 8 bit EEPROM register located at the address 7FFh. It is com- posed by 4 MSBs Address Pointer, which defines the bottom boundary address, and 4 LSBs which must be programmed at ’0’. This Address Pointer can therefore address a boundary by page of 16 bytes. The block in which the Block Address Pointer de- fines the boundary of the write protected memory is defined by the logic level applied on the PB1 and PB0 input pins: – PB1 =’0’and PB0 =’0’ select block 4 – PB1 =’0’and PB0 =’1’ select block 5 – PB1 =’1’and PB0 =’0’ select block 6 – PB1 =’1’and PB0 =’1’ select block 7 The following sequence should be used to set the Write Protection: – write the data to be protected into the top of the memory, up to, but not including, location 7FFh; – select the block by hardwiring the signals PB0 & PB1; – set the protection by writing the correct bottom boundary address in the Address Pointer (4 MSBs of location 7FFh) with bit b2 (Protect Flag) set to ’0’. Note that for a correct fonctionality of the memory, all the 4 LSBs of the Block Address Pointer must also be programmed at ’0’. The area will be pro- tected when the PRE input is taken High. Remark: The Write Protection is active if and only if the PRE input pin is driven High and the bit 2 of location 7FFh is set to ’0’. In all the other cases, the memory Block will not be protected. While the PRE input pin is read at ’0’ by the memory, the location 7FFh can be used as a normal EEPROM byte. Caution: Special attention must be used when using the protect mode together with the Multibyte Write mode (MODE input pin High). If the Multibyte Write starts at the location right below the first byte of the Write Protected area, then the instruction will write over the first 7 bytes of the Write Protected area. The area protected is therefore smaller than the content defined in the location 7FFh, by 7 bytes. This does not apply to the Page Write mode as the address counter ’roll-over’ and thus cannot go above the 16 bytes lower boundary of the protected area. BYTE WRITE DEV SEL BYTE ADDR DATA IN MULTIBYTE AND PAGE WRITE DEV SEL BYTE ADDR DATA IN 1 DATA IN 2 AI00793 DATA IN N ACK ACK ACK R/W ACK ACK ACK R/W ACK ACK Figure 9. Write Modes Sequence (ST24/25C16) 11/17 ST24/25C16, ST24/25W16 |
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Mô tả tương tự - ST25C16M5TR |
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