M50FW040 datasheet(23/53 Pages) STMICROELECTRONICS

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M50FW040

Command interface

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4.4

Program command

The Program command can be used to program a value to one address in the memory array

at a time. Two Bus Write operations are required to issue the command; the second Bus

Write cycle latches the address and data in the internal state machine and starts the

Program/Erase Controller. Once the command is issued subsequent Bus Read operations

read the Status Register. See the section on the Status Register for details on the definitions

of the Status Register bits.

If the address falls in a protected block then the Program operation will abort, the data in the

memory array will not be changed and the Status Register will output the error.

During the Program operation the memory will only accept the Read Status Register

command and the Program/Erase Suspend command. All other commands will be ignored.

Typical Program times are given in Table 12.

Note that the Program command cannot change a bit set at ‘0’ back to ‘1’ and attempting to

do so will not cause any modification on its value. The Erase command must be used to set

all of the bits in the block to ‘1’.

See Figure 18: Program flowchart and pseudo code, for a suggested flowchart on using the

Program command.

4.5

Erase command

The Erase command can be used to erase a block. Two Bus Write operations are required

to issue the command; the second Bus Write cycle latches the block address in the internal

state machine and starts the Program/Erase Controller. Once the command is issued

subsequent Bus Read operations read the Status Register. See the section on the Status

If the block is protected then the Erase operation will abort, the data in the block will not be

changed and the Status Register will output the error.

During the Erase operation the memory will only accept the Read Status Register command

and the Program/Erase Suspend command. All other commands will be ignored. Typical

Erase times are given in Table 12.

The Erase command sets all of the bits in the block to ‘1’. All previous data in the block is

lost.

See Figure 20: Erase flowchart and pseudo code, for a suggested flowchart on using the

Erase command.

4.6

Clear Status Register command

The Clear Status Register command can be used to reset bits 1, 3, 4 and 5 in the Status

Once the command is issued the memory returns to its previous mode, subsequent Bus

Read operations continue to output the same data.

The bits in the Status Register are sticky and do not automatically return to ‘0’ when a new

Program or Erase command is issued. If an error occurs then it is essential to clear any error

bits in the Status Register by issuing the Clear Status Register command before attempting

a new Program or Erase command.

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