AM29F400B datasheet(14/42 Pages) AMD

14 / 42 page

Am29F400B

COMMAND DEFINITIONS

Writing specific address and data commands or

sequences into the command register initiates device

operations. Table 5 defines the valid register command

sequences. Writing incorrect address and data

values or writing them in the improper sequence

resets the device to reading array data.

All addresses are latched on the falling edge of WE# or

CE#, whichever happens later. All data is latched on

the rising edge of WE# or CE#, whichever happens

first. Refer to the appropriate timing diagrams in the

“AC Characteristics” section.

Reading Array Data

The device is automatically set to reading array data

after device power-up. No commands are required to

retrieve data. The device is also ready to read array

data after completing an Embedded Program or

Embedded Erase algorithm.

After the device accepts an Erase Suspend command,

the device enters the Erase Suspend mode. The

system can read array data using the standard read

timings, except that if it reads at an address within

erase-suspended sectors, the device outputs status

data. After completing a programming operation in the

Erase Suspend mode, the system may once again

read array data with the same exception. See “Erase

Suspend/Erase Resume Commands” for more infor-

mation on this mode.

The system

must issue the reset command to re-

enable the device for reading array data if DQ5 goes

high, or while in the autoselect mode. See the “Reset

Command” section, next.

See also “Requirements for Reading Array Data” in the

“Device Bus Operations” section for more information.

The Read Operations table provides the read parame-

ters, and Figure 9 shows the timing diagram.

Reset Command

Writing the reset command to the device resets the

device to reading array data. Address bits are don’t

care for this command.

The reset command may be written between the

sequence cycles in an erase command sequence

before erasing begins. This resets the device to reading

array data. Once erasure begins, however, the device

ig nores re se t comma nds until the op eration is

complete.

The reset command may be written between the

sequence cycles in a program command sequence

before programming begins. This resets the device to

reading array data (also applies to programming in

Erase Suspend mode). Once programming begins,

however, the device ignores reset commands until the

operation is complete.

The reset command may be written between the

sequence cycles in an autoselect command sequence.

Once in the autoselect mode, the reset command

must

be written to return to reading array data (also applies

to autoselect during Erase Suspend).

If DQ5 goes high during a program or erase operation,

writing the reset command returns the device to

read ing array da ta (a ls o applie s du r ing Erase

Suspend).

Autoselect Command Sequence

The autoselect command sequence allows the host

system to access the manufacturer and devices codes,

and determine whether or not a sector is protected.

Table 5 shows the address and data requirements. This

method is an alternative to that shown in Table 4, which

is intended for PROM programmers and requires VID

on address bit A9.

The autoselect command sequence is initiated by

writing two unlock cycles, followed by the autoselect

command. The device then enters the autoselect

mode, and the system may read at any address any

number of times, without initiating another command

sequence.

A read cycle at address XX00h or retrieves the manu-

facturer code. A read cycle at address XX01h in word

mode (or 02h in byte mode) returns the device code. A

read cycle containing a sector address (SA) and the

address 02h in word mode (or 04h in byte mode)

returns 01h if that sector is protected, or 00h if it is

unprotected. Refer to Tables 2 and 3 for valid sector

addresses.

The system must write the reset command to exit the

autoselect mode and return to reading array data.

Word/Byte Program Command Sequence

The system may program the device by word or byte,

depending on the state of the BYTE# pin. Program-

ming is a four-bus-cycle operation. The program

command sequence is initiated by writing two unlock

write cycles, followed by the program set-up command.

The program address and data are written next, which

in turn initiate the Embedded Program algorithm. The

system is

not required to provide further controls or tim-

ings. The device automatically provides internally

generated program pulses and verify the programmed

cell margin. Table 5 shows the address and data

require m e nts fo r t he by te p r og ra m c o m m and

sequence.

When the Embedded Program algorithm is complete,

the device then returns to reading array data and

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