VV6501 datasheet(30/60 Pages) STMICROELECTRONICS

30 / 60 page

Serial Control Bus

VV6501

30/60

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

be one

greater than 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.

4.3

Types of messages

This section gives guidelines on the basic operations to read data from and write data to the serial

interface.

The serial interface supports variable length messages. A message may contain no data bytes, one

data byte or many data bytes. This data can be written to or read from common or different locations

within the sensor. The range of instructions available are detailed below.

Write no data byte, only sets the index for a subsequent read message.

Multiple location write (using auto increment index bit) for fast information transfers.

Examples of these operations are given below. A full description of the internal registers is given in

the previous section. For all examples, the slave address used is 3210 for writing and 3310 for

reading. The write address includes the read/write bit (the LSB) set to zero while this bit is set in the

read address.

4.3.1

Single location, single data write

When a random value is written to the sensor, the message looks as shown in

Figure 25.

In this example, the

fineH exposure register (index = 3210) is set to 8510. The r/w bit is set to zero for

writing and the

Inc. bit (MSB of the index byte) is set to zero to disable automatic increment of the

index after writing the value. The address index is preserved and may be used by a subsequent

read. The write message is terminated with a stop condition from the master.

4.3.2

Single location, single data read

A read message always contains the index used to get the first byte.

Figure 25: Single location, single write

Figure 26: Single location, single read

20h

32h

85h

Start

Device

Ack

address

Index

Data

Stop

21h

32h

85h

Start

Device

Ack

address

Index

Data

Stop

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