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X84640E Datasheet(PDF) 4 Page - IC MICROSYSTEMS |
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X84640E Datasheet(HTML) 4 Page - IC MICROSYSTEMS |
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4 / 22 page  X84160/640/128 4 Write Sequence A nonvolatile write sequence consists of sending a reset sequence, a 16-bit address, up to 32 bytes of data, and then a special “start nonvolatile write cycle” command sequence. The reset sequence is issued first (as described in the Reset Sequence section) to set an internal write enable latch. The address is written serially by issuing 16 separate write cycles (WE and CE LOW, OE HIGH) to the part without any read cycles between the writes. The address is sent serially, most significant bit first, on the l/O pin. Up to 32 bytes of data are written by issuing a multiple of 8 write cycles. Again, no read cycles are allowed between writes. The nonvolatile write cycle is initiated by issuing a special read/write “1”/read sequence. The first read cycle ends the page load, then the write “1” followed by a read starts the nonvolatile write cycle. The device recognizes 32- byte pages (e.g., beginning at addresses XXXXXX00000 for X84160). When sending data to the part, attempts to exceed the upper address of the page will result in the address counter “wrapping-around” to the first address on the page, where data loading can continue. For this reason, sending more than 256 consecutive data bits will result in overwriting previous data. A nonvolatile write cycle will not start if a partial or incom- plete write sequence is issued. The internal write enable latch is reset when the nonvolatile write cycle is com- pleted and after an invalid write to prevent inadvertent writes. Note that this sequence is fully static, with no spe- cial timing restrictions. The processor is free to perform other tasks on the bus whenever the chip enable pin (CE) is HIGH. Nonvolatile Write Status The status of a nonvolatile write cycle can be determined at any time by simply reading the state of the l/O pin on the device. This pin is read when OE and CE are LOW and WE is HIGH. During a nonvolatile write cycle the l/O pin is LOW. When the nonvolatile write cycle is complete, the l/O pin goes HIGH. A reset sequence can also be issued during a nonvolatile write cycle with the same result: I/O is LOW as long as a nonvolatile write cycle is in progress, and l/O is HIGH when the nonvolatile write cycle is done. Figure 2: Write Sequence CE OE WE I/O (IN) "0" "0" "1" RESET LOAD ADDRESS LOAD DATA START NONVOLATILE WRITE A8 A7 A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 I/O (OUT) 7008 FRM F05.1 WHEN ACCESSING: X84160 ARRAY: A15–A11=0 X84640 ARRAY: A15–A13=0 X84128 ARRAY: A15–A14=0 A15 A14 A13 A12 A11 A10 A9 |
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