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M29W400DT Datasheet(PDF) 13 Page - STMicroelectronics |
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M29W400DT Datasheet(HTML) 13 Page - STMicroelectronics |
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13 / 38 page  13/38 M29W400DT, M29W400DB COMMAND INTERFACE All Bus Write operations to the memory are inter- preted by the Command Interface. Commands consist of one or more sequential Bus Write oper- ations. Failure to observe a valid sequence of Bus Write operations will result in the memory return- ing to Read mode. The long command sequences are imposed to maximize data security. The address used for the commands changes de- pending on whether the memory is in 16-bit or 8- bit mode. See either Table 5, or 6, depending on the configuration that is being used, for a summary of the commands. Read/Reset Command. The Read/Reset com- mand returns the memory to its Read mode where it behaves like a ROM or EPROM, unless other- wise stated. It also resets the errors in the Status Register. Either one or three Bus Write operations can be used to issue the Read/Reset command. The Read/Reset Command can be issued, be- tween Bus Write cycles before the start of a pro- gram or erase operation, to return the device to read mode. Once the program or erase operation has started the Read/Reset command is no longer accepted. The Read/Reset command will not abort an Erase operation when issued while in Erase Suspend. Auto Select Command. The Auto Select com- mand is used to read the Manufacturer Code, the Device Code and the Block Protection Status. Three consecutive Bus Write operations are re- quired to issue the Auto Select command. Once the Auto Select command is issued the memory remains in Auto Select mode until another com- mand is issued. From the Auto Select mode the Manufacturer Code can be read using a Bus Read operation with A0 = VIL and A1 = VIL. The other address bits may be set to either VIL or VIH. The Manufacturer Code for STMicroelectronics is 0020h. The Device Code can be read using a Bus Read operation with A0 = VIH and A1 = VIL. The other address bits may be set to either VIL or VIH. The Device Code for the M29W400DT is 00EEh and for the M29W400D is 00EFh. The Block Protection Status of each block can be read using a Bus Read operation with A0 = VIL, A1 = VIH, and A12-A17 specifying the address of the block. The other address bits may be set to ei- ther VIL or VIH. If the addressed block is protected then 01h is output on Data Inputs/Outputs DQ0- DQ7, otherwise 00h is output. Program Command. The Program command can be used to program a value to one address in the memory array at a time. The command re- quires four Bus Write operations, the final write op- eration latches the address and data and starts the Program/Erase Controller. If the address falls in a protected block then the Program command is ignored, the data remains unchanged. The Status Register is never read and no error condition is given. During the program operation the memory will ig- nore 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 Cy- cles. Bus Read operations during the program op- eration 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 Regis- ter. A Read/Reset command must be issued to re- set the error condition and return to Read mode. Note that the Program command cannot change a bit set at ’0’ back to ’1’. One of the Erase Com- mands must be used to set all the bits in a block or in the whole memory from ’0’ to ’1’. Unlock Bypass Command. The Unlock Bypass command is used in conjunction with the Unlock Bypass Program command to program the memo- ry. When the access time to the device is long (as with some EPROM programmers) considerable time saving can be made by using these com- mands. Three Bus Write operations are required to issue the Unlock Bypass command. Once the Unlock Bypass command has been is- sued the memory will only accept the Unlock By- pass Program command and the Unlock Bypass Reset command. The memory can be read as if in Read mode. Unlock Bypass Program Command. The Un- lock 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 Pro- gram operation using the Program command. A protected block cannot be programmed; the oper- ation cannot be aborted and the Status Register is read. Errors must be reset using the Read/Reset command, which leaves the device in Unlock By- pass Mode. See the Program command for details on the behavior. |
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