9

4Mb Smart 3 Boot Block Flash Memory

Micron Technology, Inc., reserves the right to change products or specifications without notice.

F45_3.p65 – Rev. 3, Pub. 12/01

©2001, Micron Technology, Inc.

4Mb

SMART 3 BOOT BLOCK FLASH MEMORY

latched on the falling edge of OE# or CE#, whichever

occurs last. If the contents of the status register change

during a READ of the status register, either OE# or CE#

may be toggled while the other is held LOW to update the

output.

Following a WRITE or ERASE, the device automati-

cally enters the status register read mode. In addition, a

READ during a WRITE or ERASE produces the status

register contents on DQ0–DQ7. When the device is in the

erase suspend mode, a READ operation produces the

status register contents until another command is is-

sued. In certain other modes, READ STATUS REGIS-

TER may be given to return to the status register read

mode. All commands and their operations are described

in the Command Set and Command Execution sections.

IDENTIFICATION REGISTER

A READ of the two 8-bit device identification registers

requires the same input sequencing as a READ of the

array. WE# must be HIGH, and OE# and CE# must be

LOW. However, ID register data is output only on DQ0–

DQ7, regardless of the condition of BYTE# on the

MT28F400B3. A0 is used to decode between the two bytes

of the device ID register; all other address inputs are

“Don’t Care.” When A0 is LOW, the manufacturer com-

patibility ID is output, and when A0 is HIGH, the device

ID is output. DQ8–DQ15 are High-Z when BYTE# is LOW.

When BYTE# is HIGH, DQ8–DQ15 are 00h when the

manufacturer compatibility ID is read and 44h when the

device ID is read.

To get to the identification register read mode, READ

IDENTIFICATION may be issued while the device is in

certain other modes. In addition, the identification regis-

ter read mode can be reached by applying a super-volt-

can be read while the device is in any mode. When A9 is

mode.

INPUT OPERATIONS

The DQ pins are used either to input data to the array

or to input a command to the CEL. A command input

issues an 8-bit command to the CEL to control the mode

of operation of the device. A WRITE is used to input data

to the memory array. The following section describes

both types of inputs. More information describing how to

use the two types of inputs to write or erase the device is

provided in the Command Execution section.

COMMANDS

To perform a command input, OE# must be HIGH,

and CE# and WE# must be LOW. Addresses are “Don’t

Care” but must be held stable, except during an ERASE

CONFIRM (described in a later section). The 8-bit com-

PARAMETER BLOCKS

The two 8KB parameter blocks store less sensitive and

more frequently changing system parameters and also

may store configuration or diagnostic coding. These

No super-voltage unlock or WP# control is required.

MAIN MEMORY BLOCKS

The four remaining blocks are general-purpose

memory blocks and do not require a super-voltage on

RP# or WP# control to be erased or written. These blocks

are intended for code storage, ROM-resident applica-

tions or operating systems that require in-system update

capability.

OUTPUT (READ) OPERATIONS

The MT28F004B3 and MT28F400B3 feature three dif-

ferent types of READs. Depending on the current mode of

the device, a READ operation produces data from the

memory array, status register or device identification

register. In each of these three cases, the WE#, CE# and

OE# inputs are controlled in a similar manner. Moving

between modes to perform a specific READ is described

in the Command Execution section.

MEMORY ARRAY

To read the memory array, WE# must be HIGH, and

OE# and CE# must be LOW. Valid data is output on the

DQ pins when these conditions have been met and a

valid address is given. Valid data remains on the DQ pins

until the address changes, or until OE# or CE# goes HIGH,

whichever occurs first. The DQ pins continue to output

new data after each address transition as long as OE# and

CE# remain LOW.

The MT28F400B3 features selectable bus widths.

When the memory array is accessed as a 256K x 16, BYTE#

is HIGH, and data is output on DQ0–DQ15. To access the

memory array as a 512K x 8, BYTE# must be LOW, DQ8–

DQ14 must be High-Z, and all data must be output on

DQ0–DQ7. The DQ15/A-1 pin becomes the lowest or-

der address input so that 524,288 locations can be read.

After power-up or RESET, the device is automatically

in the array read mode. All commands and their opera-

tions are described in the Command Set and Command

Execution sections.

STATUS REGISTER

Performing a READ of the status register requires the

same input sequencing as a READ of the array except that

the address inputs are “Don’t Care.” The status register

contents are always output on DQ0–DQ7, regardless of

the condition of BYTE# on the MT28F400B3. DQ8–DQ15

are LOW when BYTE# is HIGH, and DQ8–DQ14 are High-

Z when BYTE# is LOW. Data from the status register is