W39L020

Publication Release Date: November 11, 2002

- 3 -

Revision A4

6. FUNCTIONAL DESCRIPTION

Device Bus Operation

Read Mode

The read operation of the W39L020 is controlled by #CE and #OE, both of which have to be low for

the host to obtain data from the outputs. #CE is used for device selection. When #CE is high, the chip

is de-selected and only standby power will be consumed. #OE is the output control and is used to

gate data from the output pins. The data bus is in high impedance state when either #CE or #OE is

high. Refer to the timing waveforms for further details.

Write Mode

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 addressable 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 bring #WE to logic low state, while #CE is at logic low

state and #OE is at logic high state. 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 microprocessor write timings are used.

Refer to AC Write Characteristics and the Erase/Programming Waveforms for specific timing

parameters.

Standby Mode

There are two ways to implement the standby mode on the W39L020 device, both using the #CE pin.

A CMOS standby mode is achieved with the

±0.5V. Under this condition the current

is typically reduced to less than 25

µA(max). A TTL standby mode is achieved with the #CE pin held at

In the standby mode the outputs are in the high impedance state, independent of the #OE input.

Output Disable Mode

output pins to be in a high impedance state.

Auto-select Mode

The auto-select mode allows the reading of a binary code from the device and will identify its

manufacturer and type. This mode is intended for use by programming equipment for the purpose of

automatically matching the device to be programmed with its corresponding programming algorithm.

This mode is functional over the entire temperature range of the device.

A9. Two identifier bytes may then be sequenced from the device outputs by toggling address A0 from

′t cares except A0 and A1 (see "Auto-select Codes").