VV5404 datasheet(28/54 Pages) STMICROELECTRONICS

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VV5404 & VV6404

CD5404-6404F-A

28/54

5.4

Message Interpretation

All serial interface communications with the sensor must begin with a start condition. If the start condition is followed

by a valid address byte then further communications can take place. The sensor will acknowledge the receipt of a

valid address by driving the sda wire low. The state of the read/~write bit (lsb of the address byte) is stored and the

next byte of data, sampled from sda, can be interpreted.

During a write sequence the second byte received is an address index and is used to point to one of the internal

registers. The msbit of the following byte is the index auto increment flag. If this flag is set then the serial interface will

automatically increment the index address by one location after each slave acknowledge. The master can therefore

send data bytes continuously to the slave until the slave fails to provide an acknowledge or the master terminates the

write communication with a stop condition or sends a repeated start, (Sr). If the auto increment feature is used the

master does not have to send indexes to accompany the data bytes.

As data is received by the slave it is written bit by bit to a serial/parallel register. After each data byte has been

received by the slave, an acknowledge is generated, the data is then stored in the internal register addressed by the

current index.

During a read message, the current index is read out in the byte following the device address byte. The next byte read

from the slave device are the contents of the register addressed by the current index. The contents of this register

are then parallel loaded into the serial/parallel register and clocked out of the device by scl.

At the end of each byte, in both read and write message sequences, an acknowledge is issued by the receiving

device. Although VV5404 and VV6404 is always considered to be a slave device, it acts as a transmitter when the

bus master requests a read from the sensor.

At the end of a sequence of incremental reads or writes, the terminal index value in the register will be one greater

the last location read from or written to. A subsequent read will use this index to begin retrieving data from the internal

registers.

A message can only be terminated by the bus master, either by issuing a stop condition, a repeated start condition

or by a negative acknowledge after reading a complete byte during a read operation.

address[7:1]

W bit

DATA[7:0]

Sensor acknowledges valid address

Acknowledge from slave

INDEX[6:0]

INC

DATA[7:0]

[0]

0 0 1 0 0 0 0

address

Auto increment

Index bit

Figure 18 : Serial Interface Data Format

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