M29W400DT datasheet(17/48 Pages) STMICROELECTRONICS

17 / 48 page

M29W400DT, M29W400DB

Bus operations

17/48

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.

3.7

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 2

and Table 3, Bus operations.

3.8

Block protection and blocks unprotection

Each block can be separately protected against accidental Program or Erase. Protected

blocks can be unprotected to allow data to be changed.

There are two methods available for protecting and unprotecting the blocks, one for use on

programming equipment and the other for in-system use. Block Protect and Chip Unprotect

operations are described in Appendix B: Block protection.

Table 2.

Bus operations, BYTE = VIL

(1)

X = VIL or VIH.

Operation

Address inputs

DQ15A–1, A0-A17

Data inputs/outputs

DQ14-DQ8

DQ7-DQ0

Bus Read

VIL

VIH

Cell address

Hi-Z

Data output

Bus Write

VIL

VIH

VIL

Command address

Hi-Z

Data input

Output Disable

VIH

Hi-Z

Standby

VIH

Hi-Z

Read

manufacturer code

VIL

VIH

A0 = VIL, A1 = VIL,

A9 = VID,

others VIL or VIH

Hi-Z

20h

Read device code

VIL

VIH

A0 = VIH, A1 = VIL,

A9 = VID,

others VIL or VIH

Hi-Z

EEh

(M29W400DT)

EFh

(M29W400DB)

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