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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

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 AS3644 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 20). The slave address byte is the first byte received after the master

generates the START condition. The slave address byte contains the 7-bit AS3644 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 AS3644 acknowledges the slave address +

write bit, the master transmits a register address to the AS3644. This sets the register pointer on the AS3644.

The master may then transmit zero or more bytes of data, with the AS3644 acknowledging each byte received.

The address pointer will increment after each data byte is transferred. The master generates a STOP condition

to terminate the data write.

2. Slave Transmitter Mode (Read Mode): The first byte is received and handled as in the slave receiver mode.

However, in this mode, the direction bit indicates that the transfer direction is reversed. Serial data is transmit-

ted on SDA by the AS3644 while the serial clock is input on SCL. START and STOP conditions are recognized

as the beginning and end of a serial transfer (Figure 21 and Figure 22). The slave address byte is the first byte

received after the master generates a START condition. The slave address byte contains the 7-bit AS3644

address, which is 0110000, followed by the direction bit (R/W), which, for a read, is 1.

decoding the slave address byte the device outputs an acknowledge on the SDA line. The AS3644 then

begins to transmit data starting with the register address pointed to by the register pointer. If the register

pointer is not written to before the initiation of a read mode the first address that is read is the last one stored in

the register pointer. The AS3644 must receive a “not acknowledge” to end a read.

Figure 20. Data Write - Slave Receiver Mode

2. The address for writing to the AS3644 is 60h = 01100000b

3. The address for read mode from the AS3644 is 61h = 01100001b

S

0110000

0

A

XXXXXXXX

A

AA

XXXXXXXX

XXXXXXXX

A

XXXXXXXX

P

<Slave Address>

<Word Address (n)>

<Data(n)>

<Data(n+1)>

<Data(n+X)>

S - Start

A - Acknowledge (ACK)

P - Stop

Data Transferred

(X + 1 Bytes + Acknowledge)