VD6640 datasheet(28/126 Pages) STMICROELECTRONICS

28 / 126 page

Control interface

VG6640, VD6640

28/126

DocID023597 Rev 11

message is a master write to the slave. If the lsb is set (that is, 0x21) then the message is a

master read from the slave.

Figure 10. I2C device address

All serial interface communications with the sensor must begin with a start condition. The

sensor acknowledges 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 and third bytes received

provide a 16-bit index which points to one of the internal 8-bit registers.

Figure 11. Data format (write)

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 contents of the register addressed by the current index is read

out in the byte following the device address byte. The contents of this register are parallel

loaded into the serial/parallel register and clocked out of the device by the falling edge of

SCL.

Figure 12. Data format (read)

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

issued by the receiving device (that is, the image sensor for a write and the baseband for a

read).

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

by a negative acknowledge (that is, not pulling the SDA line low) after reading a complete

byte during a read operation.

MSBit

LSBit

R/W

Camera acknowledges

Acknowledge from camera

ADDRESS[7:0]

INDEX[15:8]

INDEX[7:0]

DATA[7:0]

Ac P

0x20 (write)

Start

Stop

valid address

ADDRESS[7:0]

INDEX[15:8]

INDEX[7:0]

Ac P

0x20 (write)

ADDRESS[7:0]

DATA[7:0]

0x37 (read)

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