34VL02 datasheet(6/32 Pages) MICROCHIP

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34VL02

DS22079A-page 6

2.0

FUNCTIONAL DESCRIPTION

The 34VL02 has two Software Write-Protect features

that allow you to protect half of the array from being

written (Addresses 00h-7Fh). One command, Software

Write-Protect (SWP) will prevent writes to half of the

array and is resettable by using the Clear Software

Write-Protect (CSWP) command. The other command

is Permanent Software Write-Protect (PSWP), which is

not resettable and will permanently lock half the array

from being written to. The device still has an external

pin (WP) that allows you to protect the entire array if so

desired.

The 34VL02 supports a bidirectional 2-wire bus and

data transmission protocol. A device that sends data

onto the bus is defined as a transmitter, and a device

receiving data, as a receiver. The bus has to be

controlled by a master device, which generates the

Serial Clock (SCL), controls the bus access and gener-

ates the Start and Stop conditions, while the 34VL02

works as slave. Both master and slave can operate as

transmitter or receiver, but the master device

determines which mode is activated.

3.0

BUS CHARACTERISTICS

The following bus protocol has been defined:

• Data transfer may be initiated only when the bus

is not busy.

• During data transfer, the data line must remain

stable whenever the clock line is high. Changes in

the data line while the clock line is high will be

interpreted as a Start or Stop condition.

Accordingly, the following bus conditions have been

defined (Figure 3-1).

3.1

Bus Not Busy (A)

Both data and clock lines remain high.

3.2

Start Data Transfer (B)

A high-to-low transition of the SDA line while the clock

(SCL) is high determines a Start condition. All

commands must be preceded by a Start condition.

3.3

Stop Data Transfer (C)

A low-to-high transition of the SDA line while the clock

(SCL) is high determines a Stop condition. All

operations must be ended with a Stop condition.

3.4

Data Valid (D)

The state of the data line represents valid data when,

after a Start condition, the data line is stable for the

duration of the high period of the clock signal.

The data on the line must be changed during the low

period of the clock signal. There is one clock pulse per

bit of data.

Each data transfer is initiated with a Start condition and

terminated with a Stop condition. The number of data

bytes transferred between the Start and Stop

conditions is determined by the master device and is,

theoretically, unlimited; although only the last sixteen

will be stored when doing a write operation. When an

overwrite does occur, it will replace data in a first-in,

first-out (FIFO) fashion.

3.5

Acknowledge

Each receiving device, when addressed, is obliged to

generate an Acknowledge after the reception of each

byte. Exceptions to this rule relating to software write

protection are described in Section 7.0 “Write Protec-

tion”. The master device must generate an extra clock

pulse, which is associated with this Acknowledge bit.

The device that acknowledges has to pull down the

SDA line during the Acknowledge clock pulse in such a

way that the SDA line is stable low during the high

period of the acknowledge related clock pulse. Of

course, setup and hold times must be taken into

account. During reads, a master must signal an end-of-

data to the slave by not generating an Acknowledge bit

on the last byte that has been clocked out of the slave.

In this case, the slave (34VL02) will leave the data line

high to enable the master to generate the Stop

condition.

Note:

The 34VL02 does not generate any

Acknowledge

bits

internal

programming cycle is in progress.

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