STV-366-R01 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'STV-366-R01' PDF : 30 Pages View PDF
VT5366
Serial control bus
6.3.3
No data write followed by same location 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. In this
example, the gain value (index = 36) is read as 15.
Figure 12. No data write followed by same location read
No data write
Read data
S 20h
A
36
A Sr 21h
A
15
AP
6.3.4
NAck
from the master
Note that the read message must be terminated with a negative acknowledge (A) from the
master. A positive acknowledge at this point would indicate that a multiple read was required
and the slave would put the first bit of the next byte onto the SDA line. If this was a 0 then the
SDA would be held low and the master would not be able to issue a STOP.
Multiple data read
Figure 13. Multiple data read
Start
Device
address
Ack from slave
Stop
S
21h
A
aa
A
85
AP
Data (@current index)
Ack
from the master
NAck
from the master
Data (@current index+1)
This example assumes that a write message has already taken place. 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.
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