M29F400BT datasheet(13/40 Pages) STMICROELECTRONICS

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M29F400BT, M29F400BB

Bus operations

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Bus operations

There are five standard bus operations that control the device. These are Bus Read, Bus

Write, Output Disable, Standby and Automatic Standby. See Table 2. and Table 3., 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 affect bus operations.

3.1

Bus Read

Bus Read operations read from the memory cells, or specific registers in the Command

Interface. A valid Bus Read operation involves 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 8., Read Mode

AC Waveforms, and Table 12., Read AC Characteristics, for details of when the output

becomes valid.

3.2

Bus Write

Bus Write operations write to the Command Interface. A valid Bus Write operation begins by

setting the desired address on the Address 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 Command Interface on the rising edge of

Chip Enable or Write Enable, whichever occurs first. Output Enable must remain High, VIH,

during the whole Bus Write operation. See Figure 9. and Figure 10., Write AC Waveforms,

and Table 13. and Table 14., Write AC Characteristics, for details of the timing requirements.

3.3

Output Disable

The Data Inputs/Outputs are in the high impedance state when Output Enable is High, VIH.

3.4

Standby

When Chip Enable is High, VIH, the Data Inputs/Outputs pins are placed in the high-

impedance state and the Supply Current is reduced to the Standby level.

When Chip Enable is at VIH the Supply Current is reduced to the TTL Standby Supply

Current, ICC2. To further reduce the Supply Current to the CMOS Standby Supply Current,

ICC3, Chip Enable should be held within VCC ± 0.2V. For Standby current levels see Table

11., DC Characteristics.

During program or erase operations the memory will continue to use the Program/Erase

Supply Current, ICC4, for Program or Erase operations until the operation completes.

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