M29W640FT datasheet(12/72 Pages) STMICROELECTRONICS

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2 Signal descriptions

M29W640FT, M29W640FB

12/72

2.7

Write Enable (W)

The Write Enable, W, controls the Bus Write operation of the memory

’s Command Interface.

2.8

VPP/Write Protect (VPP/WP)

The VPP/Write Protect pin provides two functions. The VPP function allows the memory to use

an external high voltage power supply to reduce the time required for Unlock Bypass Program

operations. The Write Protect function provides a hardware method of protecting the two

outermost boot blocks. The VPP/Write Protect pin must not be left floating or unconnected.

When VPP/Write Protect is Low, VIL, the memory protects the two outermost boot blocks;

Program and Erase operations in this block are ignored while VPP/Write Protect is Low, even

when RP is at VID.

When VPP/Write Protect is High, VIH, the memory reverts to the previous protection status of

the two outermost boot blocks. Program and Erase operations can now modify the data in the

two outermost boot blocks unless the block is protected using Block Protection.

Applying VPPH to the VPP/WP pin will temporarily unprotect any block previously protected

(including the two outermost parameter blocks) using a High Voltage Block Protection

technique (In-System or Programmer technique). See Table 2: Hardware Protection for details.

When VPP/Write Protect is raised to VPP the memory automatically enters the Unlock Bypass

mode. When VPP/Write Protect returns to VIH or VIL normal operation resumes. During Unlock

Bypass Program operations the memory draws IPP from the pin to supply the programming

circuits. See the description of the Unlock Bypass command in the Command Interface section.

The transitions from VIH to VPP and from VPP to VIH must be slower than tVHVPP, see Figure 13:

Accelerated Program Timing Waveforms.

Never raise VPP/Write Protect to VPP from any mode except Read mode, otherwise the

memory may be left in an indeterminate state.

A 0.1

µF capacitor should be connected between the V

PP/Write Protect pin and the VSS Ground

pin to decouple the current surges from the power supply. The PCB track widths must be

sufficient to carry the currents required during Unlock Bypass Program, IPP.

Table 2.

Hardware Protection

VPP/WP

Function

VIL

VIH

2 outermost parameter blocks protected from

Program/Erase operations

VID

All blocks temporarily unprotected except the 2

outermost blocks

VIH or VID

VID

All blocks temporarily unprotected

VPPH

VIH or VID

All blocks temporarily unprotected

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