M29W400DT datasheet(20/48 Pages) STMICROELECTRONICS

20 / 48 page

Command interface

M29W400DT, M29W400DB

20/48

During the program operation the memory will ignore all commands. It is not possible to

issue any command to abort or pause the operation. Typical program times are given in

Table 4: Program, Erase times and Program, Erase endurance cycles. Bus Read operations

during the program operation will output the Status Register on the Data inputs/outputs. See

the section on the Status Register for more details.

After the program operation has completed the memory will return to the Read mode, unless

an error has occurred. When an error occurs the memory will continue to output the Status

Read mode.

Note that the Program command cannot change a bit set at ’0’ back to ’1’. One of the Erase

commands must be used to set all the bits in a block or in the whole memory from ’0’ to ’1’.

4.4

Unlock Bypass command

The Unlock Bypass command is used in conjunction with the Unlock Bypass Program

command to program the memory. When the access time to the device is long (as with

some EPROM programmers) considerable time saving can be made by using these

commands. Three Bus Write operations are required to issue the Unlock Bypass command.

Once the Unlock Bypass command has been issued the memory will only accept the Unlock

Bypass Program command and the Unlock Bypass Reset command. The memory can be

read as if in Read mode.

4.5

Unlock Bypass Program command

The Unlock Bypass Program command can be used to program one address in memory at

a time. The command requires two Bus Write operations, the final write operation latches

the address and data and starts the Program/Erase controller.

The Program operation using the Unlock Bypass Program command behaves identically to

the Program operation using the Program command. A protected block cannot be

programmed; the operation cannot be aborted and the Status Register is read. Errors must

be reset using the Read/Reset command, which leaves the device in Unlock Bypass mode.

See the Program command for details on the behavior.

4.6

Unlock Bypass Reset command

The Unlock Bypass Reset command can be used to return to Read/Reset mode from

Unlock Bypass mode. Two Bus Write operations are required to issue the Unlock Bypass

Reset command. Read/Reset command does not exit from Unlock Bypass mode.

4.7

Chip Erase command

The Chip Erase command can be used to erase the entire chip. Six Bus Write operations

are required to issue the Chip Erase command and start the Program/Erase controller.

If any blocks are protected then these are ignored and all the other blocks are erased. If all

of the blocks are protected the Chip Erase operation appears to start but will terminate

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