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AM29LV800B Datasheet(PDF) 14 Page - Advanced Micro Devices |
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AM29LV800B Datasheet(HTML) 14 Page - Advanced Micro Devices |
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14 / 42 page  14 Am29LV800B P R E L I M I NARY Hardware Data Protection The command sequence requirement of unlock cycles for programming or erasing provides data protection against inadvertent writes (refer to Table 5 for com- mand definitions). In addition, the following hardware data protection measures prevent accidental erasure or programming, which might otherwise be caused by spurious system level signals during VCC power-up and power-down transitions, or from system noise. Low VCC Write Inhibit When VCC is less than VLKO, the device does not ac- cept any write cycles. This protects data during VCC power-up and power-down. The command register and all internal program/erase circuits are disabled, and the device resets. Subsequent writes are ignored until VCC is greater than VLKO. The system must provide the proper signals to the control pins to prevent uninten- tional writes when VCC is greater than VLKO. Write Pulse “Glitch” Protection Noise pulses of less than 5 ns (typical) on OE#, CE# or WE# do not initiate a write cycle. Logical Inhibit Write cycles are inhibited by holding any one of OE# = VIL, CE# = VIH or WE# = VIH. To initiate a write cycle, CE# and WE# must be a logical zero while OE# is a logical one. Power-Up Write Inhibit If WE# = CE# = VIL and OE# = VIH during power up, the device does not accept commands on the rising edge of WE#. The internal state machine is automatically reset to reading array data on power-up. COMMAND DEFINITIONS Writing specific address and data commands or se- quences into the command register initiates device op- erations. Table 5 defines the valid register command sequences. Writing incorrect address and data val- ues or writing them in the improper sequence resets the device to reading array data. All addresses are latched on the falling edge of WE# or CE#, whichever happens later. All data is latched on the rising edge of WE# or CE#, whichever happens first. Refer to the appropriate timing diagrams in the “AC Characteristics” section. Reading Array Data The device is automatically set to reading array data after device power-up. No commands are required to retrieve data. The device is also ready to read array data after completing an Embedded Program or Em- bedded Erase algorithm. After the device accepts an Erase Suspend com- mand, the device enters the Erase Suspend mode. The system can read array data using the standard read timings, except that if it reads at an address within erase-suspended sectors, the device outputs status data. After completing a programming opera- tion in the Erase Suspend mode, the system may once again read array data with the same exception. See “Erase Suspend/Erase Resume Commands” for more information on this mode. The system must issue the reset command to re-ena- ble the device for reading array data if DQ5 goes high, or while in the autoselect mode. See the “Reset Com- mand” section, next. See also “Requirements for Reading Array Data” in the “Device Bus Operations” section for more information. The Read Operations table provides the read parame- ters, and Figure 13 shows the timing diagram. Reset Command Writing the reset command to the device resets the de- vice to reading array data. Address bits are don’t care for this command. The reset command may be written between the se- quence cycles in an erase command sequence before erasing begins. This resets the device to reading array data. Once erasure begins, however, the device ig- nores reset commands until the operation is complete. The reset command may be written between the se- quence cycles in a program command sequence be- fore programming begins. This resets the device to reading array data (also applies to programming in Erase Suspend mode). Once programming begins, however, the device ignores reset commands until the operation is complete. The reset command may be written between the se- quence cycles in an autoselect command sequence. Once in the autoselect mode, the reset command must be written to return to reading array data (also applies to autoselect during Erase Suspend). If DQ5 goes high during a program or erase operation, writing the reset command returns the device to read- ing array data (also applies during Erase Suspend). Autoselect Command Sequence The autoselect command sequence allows the host system to access the manufacturer and devices codes, and determine whether or not a sector is protected. Table 5 shows the address and data requirements. This method is an alternative to that shown in Table 4, which is intended for PROM programmers and requires VID on address bit A9. The autoselect command sequence is initiated by writ- ing two unlock cycles, followed by the autoselect com- |
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