L640GU53RI datasheet(28/55 Pages) AMD

28 / 55 page

Am29LV641G

June 14, 2005

ADV ANCE

I N FO RMAT I O N

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 will show 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-

d ard pro gram comma nd se que nce. The unlock

bypass command sequence is initiated by first writing

two unlock cycles. This is followed by a third write

cycle containing the unlock bypass command, 20h.

The device then enters the unlock bypass mode. A

two-cycle unlock bypass program command sequence

is all that is required to program in this mode. The first

cycle in this sequence contains the unlock bypass pro-

gram command, A0h; the second cycle contains the

program address and data. Additional data is pro-

grammed in the same manner. This mode dispenses

with the initial two unlock cycles required in the stan-

dard program command sequence, resulting in faster

total programming time. Table 10 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 4 illustrates the algorithm for the program oper-

ation. Refer to the Erase and Program Operations

table in the AC Characteristics section for parameters,

and Figure 16 for timing diagrams.

Figure 4.

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

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 for program command sequence.

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