SNLS552E September 2017 – April 2024 DS90UB953-Q1
PRODUCTION DATA
The serial control bus consists of two signals: SCL and SDA. SCL is a Serial Bus Clock Input / Output signal and the SDA is the Serial Bus Data Input / Output signal. Both SCL and SDA signals require an external pullup resistor to VI2C, chosen to be either 1.8V or 3.3V.
For the standard and fast I2C modes, a pullup resistor of RPU = 4.7kΩ is recommended, while a pullup resistor of RPU = 470Ω is recommended for the fast plus mode. However, the pullup resistor value can be additionally adjusted for capacitive loading and data rate requirements. The signals are either pulled High or driven Low. The IDX pin configures the control interface to one of two possible device addresses. A pullup resistor (RHIGH) and a pulldown resistor (RLOW) can be used to set the appropriate voltage on the IDX input pin.
The Serial Bus protocol is controlled by START, START-Repeated, and STOP phases. A START occurs when SDA transitions Low while SCL is High. A STOP occurs when SDA transitions High while SCL is also HIGH. See Figure 6-9.
To communicate with an I2C target, the host controller (controller) sends data to the target address and waits for a response. This response is referred to as an acknowledge bit (ACK). If a target on the bus is addressed correctly, the target Acknowledges (ACKs) the controller by driving the SDA bus low. If the address does not match a target address of the device, the target Not-acknowledges (NACKs) the controller by pulling the SDA High. ACKs also occur on the bus when data is being transmitted. When the controller is writing data, the target ACKs after every data byte is successfully received. When the controller is reading data, the controller ACKs after every data byte is received to let the target know that the controller wants to receive another data byte. When the controller wants to stop reading, the controller NACKs after the last data byte and creates a stop condition on the bus. All communication on the bus begins with either a start condition or a repeated start condition. All communication on the bus ends with a stop condition. A READ is shown in Figure 6-10 and a WRITE is shown in Figure 6-11.
Any I2C controller located at the serializer must support I2C clock stretching. For more information on I2C interface requirements and throughput considerations, refer to the TI application note I2C communication over FPD-Link III with bidirectional control channel (SNLA131).