M29DW323DT datasheet(13/49 Pages) STMICROELECTRONICS

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M29DW323DT, M29DW323DB

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.

The Dual Bank architecture of the M29DW323 al-

lows read/write operations in Bank A, while read

operations are being executed in Bank B or vice

versa. Write operations are only allowed in one

bank at a time.

See Tables 3 and 4, Bus Operations, for a summa-

ry. Typically glitches of less than 5ns on Chip En-

able or Write Enable are ignored by the memory

and do not affect 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 12, Read Mode AC Waveforms,

and Table 13, 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 Figures 13 and 14, Write AC

Waveforms, and Tables 14 and 15, Write AC

Characteristics, for details of the timing require-

ments.

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 12, 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 Tables 3 and 4, Bus Operations.

Block Protect and Chip Unprotect. Groups

blocks can be protected against accidental Pro-

gram or Erase. The Protection Groups are shown

in Appendix A, Tables 21 and 22, Block Address-

es. The whole chip can be unprotected to allow the

data inside the blocks to be changed.

The VPP/Write Protect pin can be used to protect

the two outermost boot blocks. When VPP/Write

Protect is at VIL the two outermost boot blocks are

protected and remain protected regardless of the

Block Protection Status or the Reset/Block Tem-

porary Unprotect pin status.

Block Protect and Chip Unprotect operations are

described in Appendix D.

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