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1.2.2

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AS3644

Datasheet - D e ta i l e d D e s c r i p t i o n

Bus Not Busy

Both data and clock lines remain HIGH.

Start Data Transfer

A change in the state of the data line, from HIGH to LOW, while the clock is HIGH, defines a START condition.

Stop Data Transfer

A change in the state of the data line, from LOW to HIGH, while the clock line is HIGH, defines the STOP condition.

Data Valid

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 START and STOP conditions are not limited, and are determined by the master device. The

information is transferred byte-wise and each receiver acknowledges with a ninth bit.

Acknowledge

Each receiving device, when addressed, is obliged to generate an acknowledge after the reception of each byte. The

master device must generate an extra clock pulse that is associated with this acknowledge bit.

A device that acknowledges must 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. 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 must leave the data line HIGH to

enable the master to generate the STOP condition.

Figure 19. Data Transfer on I

Depending upon the state of the R/W bit, two types of data transfer are possible:

1. Data transfer from a master transmitter to a slave receiver. The first byte transmitted by the master is the

slave address. Next follows a number of data bytes. The slave returns an acknowledge bit after each received

byte. Data is transferred with the most significant bit (MSB) first.

2. Data transfer from a slave transmitter to a master receiver. The master transmits the first byte (the slave

address). The slave then returns an acknowledge bit, followed by the slave transmitting a number of data

bytes. The master returns an acknowledge bit after all received bytes other than the last byte. At the end of the

last received byte, a “not acknowledge” is returned. The master device generates all of the serial clock pulses

SLAVE

ADDRESS

ACKNOWLEDGEMENT

SIGNAL FROM

RECEIVER

ACKNOWLEDGEMENT

SIGNAL FROM

RECEIVER

REPEATED IF

MORE BYTES ARE

TRANSFERRED

STOP CONDITION

OR REPEATED

START CONDITION

START

CONDITION

SCL

SDA

MSB

R/W

DIRECTION

BIT

ACK

1

2

6

78

9

1

2

3-8

89