VV6501 datasheet(31/60 Pages) STMICROELECTRONICS

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VV6501

Serial Control Bus

This example assumes that a write message has already taken place and the residual index value

is 3210. A value of 8510 is read from the fineH exposure register. Note that the read message is

terminated with a negative acknowledge (A) from the master: it is not guaranteed that the master

will be able to issue a stop condition at any other time during a read message. This is because if the

data sent by the slave is all zeros, the

sda line cannot rise, which is part of the stop condition.

4.3.3

No data write followed by same location read

When a location is to be read and the value of the stored index is not known, a write message with

no data byte must be written first, specifying the index. The read message then completes the

message sequence. To avoid relinquishing the serial to bus to another master, a repeated start

condition is asserted between the write and read messages. In this example, the

gain value (index

= 3610) is read as 1510 (see Figure 27).

As mentioned in the previous example, the read message is terminated with a negative

acknowledge (A) from the master.

4.3.4

Multiple location write

If the automatic increment bit is set (MSB of the index byte), it is possible to write data bytes to

consecutive adjacent internal registers without having to send explicit indexes prior to sending each

data byte. An auto-increment write to the exposure registers with their default values is shown in

Figure 28.

Figure 27: No data write followed by same location read

Figure 28: Multiple location write

21h

36h

21h

36h

15h

No data write

Read index and data

11h

20h

10h

C1h

Incremental write

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