S71GS256 datasheet(87/195 Pages) SPANSION

87 / 195 page

December 15, 2004 S29GLxxxN_MCP_A1

S29GLxxxN MirrorBitTM Flash Family

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Info rmat i o n

read cycles.) But DQ2 cannot distinguish whether the sector is actively erasing or

is erase-suspended. DQ6, by comparison, indicates whether the device is actively

erasing, or is in Erase Suspend, but cannot distinguish which sectors are selected

for erasure. Thus, both status bits are required for sector and mode information.

Refer to Table 13 to compare outputs for DQ2 and DQ6.

Figure 6 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# subsec-

tion. Figure 18 shows the toggle bit timing diagram. Figure 19 shows the

differences between DQ2 and DQ6 in graphical form.

Reading Toggle Bits DQ6/DQ2

Refer to Figure 6 and Figure 19 for the following discussion. Whenever the system

initially begins reading toggle bit status, 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 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 op-

eration. The system 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 toggling

just as DQ5 went high. If the toggle bit is no longer toggling, the device has suc-

cessfully completed the program or erase operation. If it is still toggling, the

device 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 determines 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, determining the status as de-

scribed in the previous paragraph. Alternatively, it may choose to perform other

system tasks. In this case, the system must start at the beginning of the algo-

rithm when it returns to determine the status of the operation (top of Figure 6).

DQ5: Exceeded Timing Limits

DQ5 indicates whether the program, erase, or write-to-buffer time has ex-

ceeded a specified internal pulse count limit. Under these conditions DQ5

produces a “1,” indicating that the program or erase cycle was not successfully

completed.

The device may output a “1” on DQ5 if the system tries to program a “1” to a

location that was previously programmed to “0.” Only an erase operation can

change a “0” back to a “1.” Under this condition, the device halts the opera-

tion, and when the timing limit has been exceeded, DQ5 produces a “1.”

In all these cases, the system must write the reset command to return the device

to the reading the array (or to erase-suspend-read if the device was previously

in the erase-suspend-program mode).

DQ3: Sector Erase Timer

After writing a sector erase command sequence, the system may read DQ3 to de-

termine whether or not erasure has begun. (The sector erase timer does not

apply to the chip erase command.) If additional sectors are selected for erasure,

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