M29DW128F datasheet(19/94 Pages) STMICROELECTRONICS

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M29DW128F

Bus operations

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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, verify the

Protection Status of the Extended Memory Block (second section), and 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

Read Electronic Signature

The memory has two codes, the Manufacturer code and the Device code used to identify

the memory. These codes can accessed by performing read operations with control signals

and addresses set as shown in Table 4 and Table 6. These codes can also be accessed by

issuing an Auto Select command (see Section 6.1.2: Auto Select command).

3.6.2

Verify Extended Block Protection Indicator

The Extended Block is divided in two sections of which one is Factory Locked and the

second one is either Customer Lockable or Customer Locked.

The Protection Status of the second section of the Extended Block (Customer Lockable or

Customer Locked) can be accessed by reading the Extended Block Protection Indicator.

This is performed by applying the signals as shown in Table 5 and Table 8. The Protection

Status of the Extended Block is then output on bits DQ7 and DQ6 of the Data Input/Outputs.

(see Table 3 and Table 6, Bus Operations).

The Protection Status of the Extended Block can also be accessed by issuing an Auto

Select command (see Section 6.1.2: Auto Select command).

3.6.3

Verify Block Protection Status

The Protection Status of a Block can be directly accessed by performing a read operation

with control signals and addresses set as shown in Table 5 and Table 8. If the Block is

protected, then 01h (in x8 mode) is output on Data Input/Outputs DQ0-DQ7, otherwise 00h

is output.

3.6.4

Hardware Block Protect

The VPP/WP pin can be used to protect the four outermost parameter blocks. When VPP/WP

is at VIL the four outermost parameter blocks are protected and remain protected regardless

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

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