L640DU21NF datasheet(27/57 Pages) AMD

27 / 57 page

January 22, 2007 22366C6

Am29LV640D/Am29LV641D

D A TA

SH EE T

Any commands written to the device during the Em-

bedded Program Algorithm are ignored. Note that a

hardware reset immediately terminates the program

operation. The program command sequence should

be reinitiated once the device returns to the read

mode, to ensure data integrity.

Programming is allowed in any sequence and across

sector boundaries. A bit cannot be programmed

from “0” back to a “1.” Attempting to do so may

cause the device to set DQ5 = 1, or cause the DQ7

and DQ6 status bits to indicate the operation was suc-

cessful. However, a succeeding read shows that the

data is still “0.” Only erase operations can convert a “0”

to a “1.”

Unlock Bypass Command Sequence

The unlock bypass feature allows the system to pro-

gram words to the device faster than using the stan-

dard program command sequence. The unlock bypass

command sequence is initiated by first writing two un-

lock cycles. This is followed by a third write cycle con-

taining the unlock bypass command, 20h. The device

then enters the unlock bypass mode. A two-cycle un-

lock bypass program command sequence is all that is

required to program in this mode. The first cycle in this

sequence contains the unlock bypass program com-

mand, A0h; the second cycle contains the program

address and data. Additional data is programmed in

the same manner. This mode dispenses with the initial

two unlock cycles required in the standard program

command sequence, resulting in faster total program-

ming time. Table 10 on page 28 shows the require-

ments for the command sequence.

During the unlock bypass mode, only the Unlock By-

pass Program and Unlock Bypass Reset commands

are valid. To exit the unlock bypass mode, the system

must issue the two-cycle unlock bypass reset com-

mand sequence. The first cycle must contain the data

90h. The second cycle must contain the data 00h. The

device then returns to the read mode.

The device offers accelerated program operations

through the ACC pin. When the system asserts V

HH on

the ACC pin, the device automatically enters the Un-

lock Bypass mode. The system may then write the

two-cycle Unlock Bypass program command se-

quence. The device uses the higher voltage on the

ACC pin to accelerate the operation. Note that the

ACC pin must not be at V

HH for operations other than

accelerated programming, or device damage may re-

sult.

Figure 3 illustrates the algorithm for the program oper-

ation. Refer to the “Erase and Program Operations” on

page 39 table in the AC Characteristics section for pa-

rameters, and Figure 15, on page 40 for timing dia-

grams.

Figure 3.

Program Operation

Chip Erase Command Sequence

Chip erase is a six bus cycle operation. The chip erase

command sequence is initiated by writing two unlock

cycles, followed by a set-up command. Two additional

unlock write cycles are then followed by the chip erase

command, which in turn invokes the Embedded Erase

algorithm. The device does not require the system to

preprogram prior to erase. The Embedded Erase algo-

rithm automatically preprograms and verifies the entire

memory for an all zero data pattern prior to electrical

erase. The system is not required to provide any con-

trols or timings during these operations. Table 10 on

page 28 shows the address and data requirements for

the chip erase command sequence.

START

Write Program

Command Sequence

Data Poll

from System

Verify Data?

Yes

Last Address?

Yes

Programming

Completed

Increment Address

Embedded

Program

algorithm

in progress

Note: See Table 10 on page 28, for program command

sequence.

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