ISL12057 Datasheet, PDF (12/17 Pages) Intersil Corporation – Low Cost and Low Power I2C RTC Real Time Clock/Calendar

ISL12057
I²C Serial Interface
The ISL12057 supports a bi-directional 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 the 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
ISL12057 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 can change only during SCL
LOW periods. SDA state changes during SCL HIGH are
reserved for indicating START and STOP conditions (see
Figure 7). On power-up of the ISL12057, 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 ISL12057 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 7). A START condition is ignored during the power-up
sequence.
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 7). A STOP condition at the end of
a read operation or at the end of a write operation to memory
only places the device in its standby mode.
An acknowledge (ACK) is a software convention used to
indicate a successful data transfer. The transmitting device,
either master or slave, releases the SDA bus after
transmitting 8 bits. During the ninth clock cycle, the receiver
pulls the SDA line LOW to acknowledge the reception of the
8 bits of data (see Figure 8).
The ISL12057 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
ISL12057 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.
SCL
SDA
START
DATA
DATA
DATA
STABLE CHANGE STABLE
STOP
FIGURE 7. VALID DATA CHANGES, START, AND STOP CONDITIONS
SCL FROM
MASTER
1
SDA OUTPUT FROM
TRANSMITTER
8
9
HIGH IMPEDANCE
SDA OUTPUT FROM
RECEIVER
HIGH IMPEDANCE
START
FIGURE 8. ACKNOWLEDGE RESPONSE FROM RECEIVER
ACK
12
FN6755.0
June 15, 2009