vt5376 STMicroelectronics, vt5376 Datasheet - Page 10

• Manufacturer Part Number: vt5376
• Description: Ultra-low Power Laser Motion Sensor For Laser Mouse Applications
• Manufacturer: STMicroelectronics

Interface
4.3
4.4
10/24
Message interpretation
All serial interface communications with the sensor must begin with a start condition. If the
start condition is followed by a valid address byte then further communications can take
place. The sensor will acknowledge 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 byte received is an address index and is used to point
to one of the internal registers. The serial interface will automatically increment the index
address by one location after each slave acknowledge. The master can therefore send data
bytes continuously to the slave until the slave fails to provide an acknowledge or the master
terminates the write communication with a stop condition or sends a repeated start , (Sr) .
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 content of the addressed register is then parallel loaded into the
serial/parallel register and clocked out of the device by scl.
At the end of each byte, in both read and write message sequences, an acknowledge is
issued by the receiving device. 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 (NAck)
after reading a complete byte during a read operation.
Type of messages
Single location, single data write
When a random value is written to the sensor, the message will look like this:
Figure 5.
The r/w bit is set to zero for writing. The write message is terminated with a stop condition
from the master.
Single 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.
Start
S
Single location, single write
Device
address
20
h
Ack
A
Index
07
h
A
Data
00
h
Stop
A
P
VT5376