ISL22349_09 Datasheet, PDF (10/13 Pages) Intersil Corporation – Quad Digitally Controlled Potentiometers

ISL22349
Shutdown Mode
The device can be put in Shutdown mode either by pulling the
SHDN pin to GND or setting the SHDN bit in the ACR register
to 0. The truth table for Shutdown mode is in Table 3.
TABLE 3.
SHDN pin
SHDN bit
Mode
High
1
Normal operation
Low
1
Shutdown
High
0
Shutdown
Low
0
Shutdown
I²C Serial Interface
The ISL22349 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 ISL22349
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 12). On power-up of the ISL22349 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 ISL22349 continuously monitors the SDA
and SCL lines for the START condition and does not
respond to any command until this condition is met. 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 12). 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 (See Figure 13).
The ISL22349 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
ISL22349 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 1010b as the four MSBs,
and the following three bits 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 4).
TABLE 4. IDENTIFICATION BYTE FORMAT
Logic values at pins A2, A1, and A0 respectively
1
0
1
0
A2 A1 A0 R/W
(MSB)
(LSB)
SCL
SDA
START
DATA
DATA
DATA
STABLE CHANGE STABLE
STOP
FIGURE 12. VALID DATA CHANGES, START AND STOP CONDITIONS
10
FN6331.3
May 28, 2009