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AS3643

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

The AS3643 supports the I

device receiving data as a receiver. The device that controls the message is called a master. The devices that are

controlled by the master are referred to as slaves. A master device that generates the serial clock (SCL), controls the

bus access, and generates the START and STOP conditions must control the bus. The AS3643 operates as a slave on

the I

maximum clock rate) are defined. The AS3643 works in both modes. Connections to the bus are made through the

open-drain I/O lines SDA and SCL.

The following bus protocol has been defined (Figure 27):



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 are interpreted as control signals.

Accordingly, the following bus conditions have been defined:

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.