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M29W641DH10ZA1T Datasheet(PDF) 10 Page - STMicroelectronics |
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M29W641DH10ZA1T Datasheet(HTML) 10 Page - STMicroelectronics |
10 / 42 page M29W641DH, M29W641DL, M29W641DU 10/42 BUS OPERATIONS There are five standard bus operations that control the device. These are Bus Read, Bus Write, Out- put Disable, Standby and Automatic Standby. See Table 2, Bus Operations, for a summary. Typically glitches of less than 5ns on Chip Enable or Write Enable are ignored by the memory and do not af- fect bus operations. Bus Read. Bus Read operations read from the memory cells, or specific registers in the Com- mand Interface. A valid Bus Read operation in- volves setting the desired address on the Address Inputs, applying a Low signal, VIL, to Chip Enable and Output Enable and keeping Write Enable High, VIH. The Data Inputs/Outputs will output the value, see Figure 9, Read Mode AC Waveforms, and Table 10, Read AC Characteristics, for details of when the output becomes valid. Bus Write. Bus Write operations write to the Command Interface. A valid Bus Write operation begins by setting the desired address on the Ad- dress Inputs. The Address Inputs are latched by the Command Interface on the falling edge of Chip Enable or Write Enable, whichever occurs last. The Data Inputs/Outputs are latched by the Com- mand Interface on the rising edge of Chip Enable or Write Enable, whichever occurs first. Output En- able must remain High, VIH, during the whole Bus Write operation. See Figure 10 and Figure 11, Write AC Waveforms, and Table 11 and Table 12, Write AC Characteristics, for details of the timing requirements. Output Disable. The Data Inputs/Outputs are in the high impedance state when Output Enable is High, VIH. Standby. When Chip Enable is High, VIH, the memory enters Standby mode and the Data In- puts/Outputs pins are placed in the high-imped- ance state. To reduce the Supply Current to the Standby Supply Current, ICC2, Chip Enable should be held within VCC ± 0.2V. For the Standby current level see Table 9, DC Characteristics. During program or erase operations the memory will continue to use the Program/Erase Supply Current, ICC3, for Program or Erase operations un- til the operation completes. 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 re- duced to the Standby Supply Current, ICC2. The Data Inputs/Outputs will still output data if a Bus Read operation is in progress. Special Bus Operations Additional bus operations can be performed to read the Electronic Signature and also to apply and remove Block Protection. These bus opera- tions are intended for use by programming equip- ment and are not usually used in applications. They require VID to be applied to some pins. Electronic Signature. The memory has two codes, the manufacturer code and the device code, that can be read to identify the memory. These codes can be read by applying the signals listed in Table 2, Bus Operations. Block Protect and Chip Unprotect. Groups of blocks can be protected against accidental Pro- gram or Erase. The whole chip can be unprotected to allow the data inside the blocks to be changed. Write Protect (WP) can be used to protect one of the outermost blocks. When Write Protect (WP) is at VIL one of the two outermost blocks is protect- ed and remains protected regardless of the Block Protection Status or the Reset/Block Temporary Unprotect pin status. For the M29W641DH, it is the highest addressed block that can be protect- ed. For the M29W641DL, it is the lowest. Block Protect and Chip Unprotect operations are described in Appendix D. |
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