VV6501 datasheet(29/60 Pages) STMICROELECTRONICS

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VV6501

Serial Control Bus

The first byte contains the device address byte which includes the data direction

read, (r), ~write,

(~w), bit.

The byte following the address byte contains the address of the first data byte (also referred to as

the

index). The serial interface can address up to 128 byte registers. If the MSB of the second byte

is set, the automatic increment feature of the address index is selected.

4.2.2

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 MSB 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

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 VV6501 is always considered to be a slave device, it acts as a

transmitter when the bus master requests a read from the sensor.

Figure 23: VV6501 Serial interface address

Figure 24: Serial interface data format

R/W

address[7:1]

W bit

DATA[7:0]

Sensor acknowledges valid address

Acknowledge from slave

INDEX[6:0]

INC

DATA[7:0]

[0]

address

Auto increment

Index bit

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