THS7353 Datasheet, PDF (34/51 Pages) Texas Instruments – 3-Channel Low Power Video Buffer with I2C Control, Selectable Filters, External Gain Control, 2:1 Input MUX, and Selectable Input Modes

THS7353
SLOS484 – NOVEMBER 2005
www.ti.com
I²C INTERFACE NOTES
APPLICATION INFORMATION (continued)
The I²C interface is used to access the internal registers of the THS7353. I²C is a two-wire serial interface
developed by Philips Semiconductor (see the I²C-Bus Specification, Version 2.1, January 2000). The bus
consists of a data line (SDA) and a clock line (SCL) with pull-up structures. When the bus is idle, both SDA and
SCL lines are pulled high. All the I²C compatible devices connect to the I²C bus through open drain I/O pins,
SDA and SCL. A master device, usually a microcontroller or a digital signal processor, controls the bus. The
master is responsible for generating the SCL signal and device addresses. The master also generates specific
conditions that indicate the START and STOP of data transfer. A slave device receives and/or transmits data on
the bus under control of the master device. The THS7353 works as a slave and supports the standard mode
transfer (100 kbps) and fast mode transfer (400 kbps) as defined in the I²C-Bus specification. The THS7353 has
been tested to be fully functional but not ensured with the high-speed mode (3.4 Mbps).
The basic I²C start and stop access cycles are shown in Figure 70.
The basic access cycle consists of the following:
• A start condition
• A slave address cycle
• Any number of data cycles
• A stop condition
SDA
SCL
S
P
Start
Condition
Stop
Condition
Figure 70. I²C Start and Stop Conditions
GENERAL I²C PROTOCOL
• The master initiates data transfer by generating a start condition. The start condition exist when a high-to-low
transition occurs on the SDA line while SCL is high, as shown in Figure 70. All I²C-compatible devices should
recognize a start condition.
• The master then generates the SCL pulses and transmits the 7-bit address and the read/write direction bit
R/W on the SDA line. During all transmissions, the master ensures that data is valid. A valid data condition
requires the SDA line to be stable during the entire high period of the clock pulse (see Figure 71). All devices
recognize the address sent by the master and compare it to their internal fixed addresses. Only the slave
device with a matching address generates an acknowledge (see Figure 72) by pulling the SDA line low
during the entire high period of the ninth SCL cycle. On detecting this acknowledge, the master knows that a
communication link with a slave has been established.
• The master generates further SCL cycles to either transmit data to the slave (R/W bit 1) or receive data from
the slave (R/W bit 0). In either case, the receiver needs to acknowledge the data sent by the transmitter. So,
an acknowledge signal can either be generated by the master or by the slave, depending on which one is the
receiver. The 9-bit valid data sequences consisting of 8-bit data and 1-bit acknowledge can continue as long
as necessary (See Figure 73).
• To signal the end of the data transfer, the master generates a stop condition by pulling the SDA line from low
to high while the SCL line is high (see Figure 70). This releases the bus and stops the communication link
with the addressed slave. All I²C compatible devices must recognize the stop condition. Upon the receipt of a
stop condition, all devices know that the bus is released, and they wait for a start condition followed by a
matching address.
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