ISL23345
15
FN7872.0
June 21, 2011
I2C Serial Interface
The ISL23345 supports an I2C bidirectional bus oriented
protocol. The protocol defines any device that sends data onto
the bus as a transmitter and the receiving device as the receiver.
The device controlling the transfer is a master and the device
being controlled is the slave. The master always initiates data
transfers and provides the clock for both transmit and receive
operations. Therefore, the ISL23345 operates as a slave device
in all applications.
All communication over the I2C interface is conducted by sending
the MSB of each byte of data first.
Protocol Conventions
Data states on the SDA line must change only during SCL LOW
periods. SDA state changes during SCL HIGH are reserved for
indicating START and STOP conditions (see Figure
27). On
power-up of the ISL23345, the SDA pin is in the input mode.
All I2C interface operations must begin with a START condition,
which is a HIGH-to-LOW transition of SDA while SCL is HIGH. The
ISL23345 continuously monitors the SDA and SCL lines for the
START condition and does not respond to any command until this
condition is met (see Figure
27). A START condition is ignored
during the power-up of the device.
All I2C interface operations must be terminated by a STOP
condition, which is a LOW to HIGH transition of SDA while SCL is
HIGH (see Figure
27). A STOP condition at the end of a read
operation or at the end of a write operation places the device in
its standby mode.
An ACK (Acknowledge) is a software convention used to indicate
a successful data transfer. The transmitting device, either master
or slave, releases the SDA bus after transmitting eight bits.
During the ninth clock cycle, the receiver pulls the SDA line LOW
to acknowledge the reception of the eight bits of data
The ISL23345 responds with an ACK after recognition of a START
condition followed by a valid Identification Byte, and once again
after successful receipt of an Address Byte. The ISL23345 also
responds with an ACK after receiving a Data Byte of a write
operation. The master must respond with an ACK after receiving
a Data Byte of a read operation.
A valid Identification Byte contains 1010 as the four MSBs, and
the following three bits are matching the logic values present at
pins A2, A1 and A0. The LSB is the Read/Write bit. Its value is “1”
for a Read operation and “0” for a Write operation (see Table
3).TABLE 3. IDENTIFICATION BYTE FORMAT
FIGURE 26. SHUTDOWN MODE WIPER RESPONSE
POWER-UP
USER PROGRAMMED
MID SCALE = 80H
SHDN ACTIVATED SHDN RELEASED
AFTER SHDN
W
IPE
R
V
O
LT
AGE,
V
RW
(V)
SHDN MODE
TIME (s)
WIPER RESTORE TO
THE ORIGINAL POSITION
0
1010
A2
A1
A0
R/W
(MSB)
(LSB)
LOGIC VALUES AT PINS A2, A1 AND A0 RESPECTIVELY
SDA
SCL
START
DATA
STOP
STABLE
CHANGE
DATA
STABLE
FIGURE 27. VALID DATA CHANGES, START AND STOP CONDITIONS