M95256-D-CS3TGSLASHA datasheet(10/48 Pages) STMICROELECTRONICS

10 / 48 page

Signal description

M95256-DR, M95256, M95256-W, M95256-R

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Doc ID 12276 Rev 11

3.6

Write Protect (W)

The main purpose of this input signal is to freeze the size of the area of memory that is

protected against Write instructions (as specified by the values in the BP1 and BP0 bits of

the Status Register).

This pin must be driven either high or low, and must be stable during all write instructions.

3.7

VSS ground

VSS is the reference for the VCC supply voltage.

3.8

Operating supply voltage (VCC)

Prior to selecting the memory and issuing instructions to it, a valid and stable VCC voltage

within the specified [VCC(min), VCC(max)] range must be applied (see Table 8, Table 9,

Table 10).

This voltage must remain stable and valid until the end of the transmission of the

instructionand, for a Write instruction, until the completion of the internal write cycle (tW).

In order to secure a stable DC supply voltage, it is recommended to decouple the VCC line

with a suitable capacitor (usually of the order of 10 nF to 100 nF) close to the VCC/VSS

package pins.

3.8.1

Device reset

In order to prevent inadvertent write operations during power-up, a power-on-reset (POR)

circuit is included. At power-up, the device does not respond to any instruction until VCC

reaches the internal Reset threshold voltage (this threshold is defined in DC tables as

VRES). (this threshold is lower than the minimum VCC operating voltage defined in Table 8,

Table 9 and Table 10).

When VCC passes over the POR threshold, the device is reset and in the following state:

●

in Standby Power mode,

●

deselected (note that a further instruction must be preceded by a falling edge on Chip

Select (S) to be executed),

●

Status Register value:

–

the Write Enable Latch (WEL) is reset to 0,

–

Write In Progress (WIP) is reset to 0,

–

The SRWD, BP1 and BP0 bits remain unchanged (non-volatile bits)

When VCC passes over the POR threshold, the device is reset and enters the Standby

Power mode, however, the device must not be accessed until VCC reaches a valid and

stable VCC voltage within the specified [VCC(min), VCC(max)] range defined in Table 8, Table 9

and Table 10).

3.8.2

Power-up conditions

When the power supply is turned on, VCC rises continuously from VSS to VCC. During this

time, the Chip Select (S) line is not allowed to float but should follow the VCC voltage, it is

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