W39L020

Publication Release Date: November 11, 2002

- 5 -

Revision A4

Logical Inhibit

#CE and #WE must be a logical zero while #OE is a logical one.

Power-up Write and Read Inhibit

edge of #WE except 5mS delay (see the power up timing in AC Characteristics). The internal state

machine is automatically reset to the read mode on power-up.

Command Definitions

Device operations are selected by writing specific address 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. "Command Definitions" defines the valid register command sequences.

Read Command

The device will automatically power-up in the read state. In this case, a command sequence is not

required to read data. Standard microprocessor read cycles will retrieve array data. This default value

ensures that no spurious alteration of the memory content occurs during the power transition.

The device will automatically returns to read state after completing an Embedded Program or

Embedded Erase algorithm.

Refer to the AC Read Characteristics and Waveforms for the specific timing parameters.

Auto-select Command

Flash memories are intended for use in applications where the local CPU can alter memory contents.

As such, manufacture and device codes must be accessible while the device resides in the target

system. PROM programmers typically access the signature codes by raising A9 to a high voltage.

However, multiplexing high voltage onto the address lines is not generally a desirable system design

practice.

The device contains an auto-select command operation to supplement traditional PROM programming

methodology. The operation is initiated by writing the auto-select command sequence into the

command register. Following the command write, a read cycle from address XX00H retrieves the

manufacture code of DAH. A read cycle from address XX01H returns the device code (W39L020 =

B5hex).

To terminate the operation, it is necessary to write the auto-select exit command sequence into the

register.

Byte Program Command

The device is programmed on a byte-by-byte basis. Programming 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. Addresses are latched on the falling edge of #CE or #WE, whichever happens

later and the data is latched on the rising edge of #CE or #WE, whichever happens first. The rising

edge of #CE or #WE (whichever happens first) begins programming using the Embedded Program