M29W640FT datasheet(16/72 Pages) STMICROELECTRONICS

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3 Bus operations

M29W640FT, M29W640FB

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3.5

Automatic Standby

If CMOS levels (VCC ± 0.2V) are used to drive the bus and the bus is inactive for 300ns or more

the memory enters Automatic Standby where the internal Supply Current is reduced to the

Standby Supply Current, ICC2. The Data Inputs/Outputs will still output data if a Bus Read

operation is in progress.

3.6

Special Bus Operations

Additional bus operations can be performed to read the Electronic Signature and also to apply

and remove Block Protection. These bus operations are intended for use by programming

equipment and are not usually used in applications. They require VID to be applied to some

pins.

3.6.1

Electronic Signature

The memory has two codes, the manufacturer code and the device code, that can be read to

identify the memory. These codes can be read by applying the signals listed in Table 3: Bus

Operations, BYTE = VIL and Table 4: Bus Operations, BYTE = VIH.

3.6.2

Block Protect and Chip Unprotect

Groups of blocks can be protected against accidental Program or Erase. The Protection

Groups are shown in Appendix A: Block addresses Table 20 and Table 21. The whole chip can

be unprotected to allow the data inside the blocks to be changed.

The VPP/Write Protect pin can be used to protect the two outermost boot blocks. When VPP/

Write Protect is at VIL the two outermost boot blocks are protected and remain protected

regardless of the Block Protection Status or the Reset/Block Temporary Unprotect pin status.

Block Protect and Chip Unprotect operations are described in Appendix D: Block Protection.

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