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38 / 63 page 36 Am49LV6408M November 5, 2003 ADV ANCE I N FO RMAT I O N Figure 9. Toggle Bit Algorithm DQ2: Toggle Bit II The “Toggle Bit II” on DQ2, when used with DQ6, indi- cates whether a particular sector is actively erasing (that is, the Embedded Erase algorithm is in progress), or whether that sector is erase-suspended. Toggle Bit II is valid after the rising edge of the final WE# pulse in the command sequence. DQ2 toggles when the system reads at addresses within those sectors that have been selected for era- sure. (The system may use either OE# or CE# to con- trol the read cycles.) But DQ2 cannot distinguish whether the sector is actively erasing or is erase-sus- pended. DQ6, by comparison, indicates whether the device is actively erasing, or is in Erase Suspend, but cannot distinguish which sectors are selected for era- sure. Thus, both status bits are required for sector and mode information. Refer to Table 12 to compare out- puts for DQ2 and DQ6. Figure 9 shows the toggle bit algorithm in flowchart form, and the section “DQ2: Toggle Bit II” explains the algorithm. See also the RY/BY#: Ready/Busy# sub- section. Figure 21 shows the toggle bit timing diagram. Figure 22 shows the differences between DQ2 and DQ6 in graphical form. Reading Toggle Bits DQ6/DQ2 Refer to Figure 9 for the following discussion. When- ever the system initially begins reading toggle bit sta- tus, it must read DQ7–DQ0 at least twice in a row to determine whether a toggle bit is toggling. Typically, the system would note and store the value of the tog- gle bit after the first read. After the second read, the system would compare the new value of the toggle bit with the first. If the toggle bit is not toggling, the device has completed the program or erase operation. The system can read array data on DQ7–DQ0 on the fol- lowing read cycle. However, if after the initial two read cycles, the system determines that the toggle bit is still toggling, the sys- tem also should note whether the value of DQ5 is high (see the section on DQ5). If it is, the system should then determine again whether the toggle bit is tog- gling, since the toggle bit may have stopped toggling just as DQ5 went high. If the toggle bit is no longer toggling, the device has successfully completed the program or erase operation. If it is still toggling, the de- vice did not completed the operation successfully, and the system must write the reset command to return to reading array data. The remaining scenario is that the system initially de- termines that the toggle bit is toggling and DQ5 has not gone high. The system may continue to monitor the toggle bit and DQ5 through successive read cy- cles, determining the status as described in the previ- ous paragraph. Alternatively, it may choose to perform START No Yes Yes DQ5 = 1? No Yes Toggle Bit = Toggle? No Program/Erase Operation Not Complete, Write Reset Command Program/Erase Operation Complete Read DQ7–DQ0 Toggle Bit = Toggle? Read DQ7–DQ0 Twice Read DQ7–DQ0 Note: The system should recheck the toggle bit even if DQ5 = “1” because the toggle bit may stop toggling as DQ5 changes to “1.” See the subsections on DQ6 and DQ2 for more information. |
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