VS6724 datasheet(46/118 Pages) STMICROELECTRONICS

46 / 118 page

Host communication - I²C control interface

VS6724

46/118

Figure 33. Random location, single write

3.3.2

Current location, single data read

For the master reading from the slave the R/W bit is set to one. The register index of the

data returned is that accessed by the previous read or write message.

The first data byte returned by a read message is the contents of the internal index value

and NOT the index value. This was the case in older V2W implementations.

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.

Figure 34. Current location, single read

3.3.3

Random location, single data read

When a location is to be read, but 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.

DEV ADDR R/W A

DATA

A/A

DATA

INDEX[7:0]

DATA[7:0]

INDEX[15:8]

Previous Index Value, K

Index M

16-bit Index, 8-bit Data, Random Location, Single Data Write

Index[15:0]

value, M

DATA[7:0]

From Master to Slave

From Slave to Master

S = START condition

Sr = repeated START

P = STOP Condition

A = Acknowledge

A = Negative acknowledge

‘0’ (Write)

DATA

DATA[7:0]

DEV ADDR R/W A

‘1’ (Read)

Previous Index Value, K

16-bit index, 8-bit data current location, single data read

From Master to Slave

From Slave to Master

S = START Condition

Sr = repeated START

P = STOP Condition

A = Acknowledge

A = Negative Acknowledge

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