AM29LV800T datasheet(14/48 Pages) AMD

14 / 48 page

Am29LV800T/Am29LV800B

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 Protect

Sectors of the Am29LV800 may be hardware pro-

tected at the user’s factory with external programming

equipment. The protection circuitry will disable both

program and erase functions for the protected sec-

tors, making the protected sectors read-only. Re-

quests to program or erase a protected sector will be

ignored by the device. 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 protected 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 pro-

tected 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 Am29LV800 may be temporarily

unprotected by raising the RESET pin to 12.0 Volts

(VID). During this mode, formerly protected sectors

can be programmed or erased with standard com-

mand sequences by selecting the appropriate byte or

sector addresses. Once the RESET pin goes to TTL

level (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 writing

them in the improper sequence will reset the device

to the read mode. Table 6 deﬁnes the valid register

command sequences. Note that the Erase Suspend

(B0h) and Erase Resume (30h) commands 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

Am29LV800 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

XX01hreturns the device code DAh/5Bh for x8 conﬁgu-

ration or 22DAh/225Bh for x16 conﬁguration (see Table

3). All manufacturer and device codes will exhibit odd

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

the parity bit. Scanning the sector addresses (A12,

A13, A14, A15, A16, A17, and A18) while (A6, A1, A0)

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

DQ0 for a write protected sector (See Table 3).

To terminate the Autoselect operation, it is neces-

sary to write the read/reset command sequence

into the register.

RESET

+12.0 V

500 ns min.

20478D-8

Figure 1.

Temporary Sector Unprotect Timing Diagram

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