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1.2-2

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AS3642

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

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 20. 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

and the START and STOP conditions. A transfer is ended with a STOP condition or with a repeated START

condition. Since a repeated START condition is also the beginning of the next serial transfer, the bus is not

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

The AS3642 can operate in the following two modes:

1. Slave Receiver Mode (Write Mode): Serial data and clock are received through SDA and SCL. After each

byte is received an acknowledge bit is transmitted. START and STOP conditions are recognized as the begin-

ning and end of a serial transfer. Address recognition is performed by hardware after reception of the slave

address and direction bit (see Figure 21). The slave address byte is the first byte received after the master

generates the START condition. The slave address byte contains the 7-bit AS3642 address, which is 0110000,

followed by the direction bit (R/W), which, for a write, is 0.

byte the device outputs an acknowledge on the SDA line. After the AS3642 acknowledges the slave address +

write bit, the master transmits a register address to the AS3642. This sets the register pointer on the AS3642.

The master may then transmit zero or more bytes of data, with the AS3642 acknowledging each byte received.

5. The address for writing to the AS3642 is 60h = 01100000b

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