AM29LV008T データシートの表示（PDF） - Advanced Micro Devices

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AM29LV008T

8 Megabit (1,048,576 x 8-Bit) CMOS 3.0 Volt-only, Sectored Flash Memory

Advanced Micro Devices 

PRELIMINARY

Write

Device erasure and programming are accomplished

via the command register. The command register is

written by bringing WE to VIL, while CE is at VIL and OE

is at VIH. Addresses are latched on the falling edge of

CE or WE, whichever occurs later, while data is latched

on the rising edge of the CE or WE pulse, whichever

occurs first. Standard microprocessor write timings are

used.

Refer to AC Write Characteristics and the Erase/

Programming Waveforms for specific timing parameters.

Sector Protection

Sectors of the Am29LV008 may be hardware protected

at the user’s factory with external programming equip-

ment. The protection circuitry will disable both program

and erase functions for the protected sectors, making

the protected sectors read-only. Requests to program

or erase a protected sector will be ignored by the de-

vice. If the user attempts to write to a protected sector,

DATA Polling will be activated for about 1 µs; the device

will then return to read mode, with data from the pro-

tected sector unchanged. If the user attempts to erase

a protected sector, Toggle Bit will be activated for about

50 µs; the device will then return to read mode, without

having erased the protected sector.

It is possible to determine if a sector is protected in the

system by writing an Autoselect command. Performing

a read operation at the address location XX02H, where

the higher order address A18–A12 represents the sec-

tor address, will produce a logical ‘1’ at DQ0 for a pro-

tected sector.

Temporary Sector Unprotect

The sectors of the Am29LV008 may be temporarily un-

protected by raising the RESET pin to 12.0 volts (VID).

During this mode, formerly protected sectors can be

programmed or erased with standard command se-

quences by selecting the appropriate byte or sector ad-

dresses. Once the RESET pin goes to VIH, all the

previously protected sectors will be protected again.

Command Definitions

Device operations are selected by writing specific ad-

dress and data sequences into the command register.

Writing incorrect address and data values or writ-

ing them in the improper sequence will reset the

device to the read mode. Table 5 on page 13 defines

the valid register command sequences. Note that the

Erase Suspend (B0H) and Erase Resume (30H) com-

mands are valid only while the Sector Erase operation

is in progress.

Read/Reset Command

The device will automatically power up in the read/

reset state. In this case, a command sequence is

not required to read data. Standard microproces-

sor cycles will retrieve array data. This default

value ensures that no spurious alteration of the

memory content occurs during the power transi-

tion. Refer to the AC Characteristics section for the

specific timing parameters.

The read or reset operation is initiated by writing the

read/reset command sequence into the command reg-

ister. Microprocessor read cycles retrieve array data

from the memory. The device remains enabled for

reads until the command register contents are altered.

Autoselect Command

Flash memories are intended for use in applications

where the local CPU alters memory contents. As such,

manufacturer and device codes must be accessible

while the device resides in the target system. The

Am29LV008 contains an autoselect command opera-

tion that provides device information and sector protec-

tion status to the system. The operation is initiated by

writing the autoselect command sequence into the

command register. Following the command write, a

read cycle from address XX00H retrieves the manufac-

turer code of 01H. A read cycle from address XX01H

returns the device code 3EH (for top boot device) or

37H (for bottom boot device); see Table 2 on page 9.

All manufacturer and device codes will exhibit odd par-

ity with the MSB of the lower byte (DQ7) defined as the

parity bit. Scanning the sector addresses (A13, A14,

A15, A16, A17, A18, and A19) while (A6, A1, A0) = (0,

1, 0) will produce a logical ‘1’ code at device output

DQ0 for a write protected sector (See Table 2).

To terminate the Autoselect operation, it is neces-

sary to write the read/reset command sequence

into the register.

12

Am29LV008T/Am29LV008B

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