AM29F800T datasheet(12/41 Pages) AMD

12 / 41 page

Am29F800T/Am29F800B

8/18/97

PR E L IM IN A R Y

Write

Device erasure and programming are accomplished

via the command register. The contents of the register

serve as inputs to the internal state machine. The state

machine outputs dictate the function of the device.

The command register itself does not occupy any ad-

dressable memory location. The register is a latch used

to store the commands, along with the address and

data information needed to execute the command. The

command register is written to by bringing WE to VIL,

while CE is at VIL and OE is at VIH. Addresses are

latched on the falling edge of WE or CE, whichever

happens later; while data is latched on the rising edge

of WE or CE, whichever happens first. Standard micro-

processor write timings are used.

Refer to AC Write Characteristics and the Erase/Pro-

gramming Waveforms for specific timing parameters.

Sector Protection

The Am29F800 features hardware sector protection.

This feature will disable both program and erase oper-

ations in any combination of nineteen sectors of mem-

ory. The sector protect feature is enabled using

programming equipment at the user’s site. The device

is shipped with all sectors unprotected. Alternatively,

AMD may program and protect sectors in the factory

prior to shipping the device (AMD’s ExpressFlash™

Service).

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 bits A12–A18 is the desired

sector address, will produce a logical “1” at DQ0 for a

protected sector. See Table 3 for Autoselect codes.

Temporary Sector Unprotect

This feature allows temporary unprotection of previ-

ously protected sectors of the Am29F800 device in

order to change data in-system. The Sector Unprotect

mode is activated by setting the RESET pin to high volt-

age (12 V). During this mode, formerly protected sec-

tors can be programmed or erased by selecting the

sector addresses. Once the 12 V is taken away from

the RESET pin, all the previously protected sectors will

be protected again. Refer to Figures 17 and 18.

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 7 defines the valid

Suspend (B0H) and Erase Resume (30H) commands

are valid only while the Sector Erase operation is in

progress. Moreover, both Reset/Read commands are

functionally equivalent, resetting the device to the

read mode.

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