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M29W640FT Datasheet(PDF) 12 Page - Numonyx B.V |
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M29W640FT Datasheet(HTML) 12 Page - Numonyx B.V |
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12 / 71 page  Signal descriptions M29W640FT, M29W640FB 12/71 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 3: 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 0.1µF capacitor should be connected between the VPP/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 3. Hardware protection VPP/WP RP 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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