BLOCK ERASE

The Block Erase sequence erases a specified block (4 kB)

of data Flash memory devices require that a block be in an

erased state prior to writing to a memory cell In this man-

ner a block must be erased prior to the recording of any

messages or storage of any images

TLD12475 – 7

FIGURE 4 Block Erase Sequence

Functional Description

ORGANIZATION

The NM29A040080 are 4-Mbit and 8-Mbit devices respec-

tively organized as 128256 blocks of 128 pages A block is

the smallest unit that can be erased and is 4 kbytes in size

Within a block are 16 rows of 8 pages each row 256 bytes

long Each page is 32 bytes long Read and write operations

always operate on a page at a time

TLD12475 – 8

FIGURE 5 Device Organization

Reading or writing data to the Serial Flash involves clocking

data into or out of the data register The data register is a

32-byte wide shift register equivalent in size to one page

When shifting in a full page writing to the array and then

reading out the same page the first bit shifted in will be the

first bit shifted out If for example only 5 bytes are shifted in

written to the array and then the same page is read out 27

bytes should be shifted out before the original 5 bytes will

be shifted out See Note 4 in the notifications section for an

explanation of multiple page writes and masking

TLD12475 – 9

FIGURE 6 Block Organization

WRITE ONCE BLOCK

The NM29A040 contains 127 blocks (blocks 0 thru block

126) which are fully accessible to the user for reading writ-

ing and erasing The final block number 127 has been set

aslde as a write once block The pages in this block may

only be written to once Once the data is written it may not

be erased In this manner block 127 may be used for stor-

ing system configuration information that cannot be lost

The NM29A080 operates in a similar manner but has 253

blocks that are fully accessible Block 254 contains the un-

usable block information although this block has 256 pages

as opposed to the standard 128 pages

The last block is not accessible through the normal Read

and Write commands Special commands for Read (D0H)

and Write (F0H) are used to perform the last block opera-

tions An erase operation is not available or usable on the

last block

DATA REGISTER

The data register is a 32-byte FIFO that is used to shift data

into or out of the device When a write operation is per-

formed all 32 bytes are written to the currently addressed

page Refer to Note 4 for how to write less than 32 bytes to

a page

The data register may be used as an on-chip holding area

for partial page data For example if data is acquired exter-

nally in 8-byte multiples the data register can be used to

hold each 8-byte segment After the 4th such data segment

an entire page of data will have been accumulated at which

point the write command mat be issued No data may be

shifted into or out of the data register while the device is

busy

READYBUSY OUTPUT

When the Serial Flash device is selected with CS held low

then the DO pin reflects the ReadyBusy state of the de-

vice This is true at all times except when reading data out

of the device as in the Get-Status command or the Data-

Shift-Out command When the device is unselected the DO

output is in a high impedance state

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