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AM29F040B Datasheet(PDF) 14 Page - Advanced Micro Devices |
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AM29F040B Datasheet(HTML) 14 Page - Advanced Micro Devices |
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14 / 30 page  14 Am29F040B P R E L I M I NARY DQ6: Toggle Bit I Toggle Bit I on DQ6 indicates whether an Embedded Program or Erase algorithm is in progress or complete, or whether the device has entered the Erase Suspend mode. Toggle Bit I may be read at any address, and is valid after the rising edge of the final WE# pulse in the command sequence (prior to the program or erase op- eration), and during the sector erase time-out. During an Embedded Program or Erase algorithm op- eration, successive read cycles to any address cause DQ6 to toggle. (The system may use either OE# or CE# to control the read cycles.) When the operation is complete, DQ6 stops toggling. After an erase command sequence is written, if all sectors selected for erasing are protected, DQ6 tog- gles for approximately 100 µs, then returns to reading array data. If not all selected sectors are protected, the Embedded Erase algorithm erases the unpro- tected sectors, and ignores the selected sectors that are protected. The system can use DQ6 and DQ2 together to deter- mine whether a sector is actively erasing or is erase- suspended. When the device is actively erasing (that is, the Embedded Erase algorithm is in progress), DQ6 toggles. When the device enters the Erase Suspend mode, DQ6 stops toggling. However, the system must also use DQ2 to determine which sectors are erasing or erase-suspended. Alternatively, the system can use DQ7 (see the subsection on “DQ7: Data# Polling”). If a program address falls within a protected sector, DQ6 toggles for approximately 2 µs after the program command sequence is written, then returns to reading array data. DQ6 also toggles during the erase-suspend-program mode, and stops toggling once the Embedded Pro- gram algorithm is complete. The Write Operation Status table shows the outputs for Toggle Bit I on DQ6. Refer to Figure 4 for the toggle bit algorithm, and to the Toggle Bit Timings figure in the “AC Characteristics” section for the timing diagram. The DQ2 vs. DQ6 figure shows the differences be- tween DQ2 and DQ6 in graphical form. See also the subsection on “DQ2: Toggle Bit II”. 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 5 to compare outputs for DQ2 and DQ6. Figure 4 shows the toggle bit algorithm in flowchart form, and the section “DQ2: Toggle Bit II” explains the algorithm. See also the “DQ6: Toggle Bit I” subsection. Refer to the Toggle Bit Timings figure for the toggle bit timing diagram. The DQ2 vs. DQ6 figure shows the dif- ferences between DQ2 and DQ6 in graphical form. Reading Toggle Bits DQ6/DQ2 Refer to Figure 4 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, a system would note and store the value of the toggle 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 sys- tem can read array data on DQ7–DQ0 on the following read cycle. However, if after the initial two read cycles, the system determines that the toggle bit is still toggling, the system 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 toggling, since the toggle bit may have stopped tog- gling 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 device did not complete 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 cycles, de- termining the status as described in the previous para- graph. Alternatively, it may choose to perform other system tasks. In this case, the system must start at the beginning of the algorithm when it returns to determine the status of the operation (top of Figure 4). DQ5: Exceeded Timing Limits DQ5 indicates whether the program or erase time has exceeded a specified internal pulse count limit. Under these conditions DQ5 produces a “1.” This is a failure condition that indicates the program or erase cycle was not successfully completed. |
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