Interpreting I2C Signal Data

Two signals are as shown in the diagram below. What are the names of the two signals? Determine the data present on the I2C signal below.

Solution

Signal A is the SDA (Serial Data) signal while signal B is the SCL (Serial Clock) signal. A start occurs when the SDA line drops when the SCK is HIGH. Data is read at the rising edge of the clock. An ACK (Acknowledgement) is sent when two byte data have been read. A stop occurs when the SDA line rises when the clock is HIGH. The interpretation is as shown by the diagram below.

Therefore the interpreted I2C signal is A4FA in hexadecimal as represented by the diagram

I2C Bus Pull-up Resistors

If the maximum permitted rise time for both the serial data (SDA) and serial clock (SCL) line of an I2C bus is 1000ns, the load capacitance is 200pF, and the minimum logic high voltage is 3.3V. The maximum acceptable values of the pull-up resistors to be used is calculated as:

Where:
t = Maximum time
C = Load Capacitance
Vth = Minimum logic high voltage
Vcc = Supply Voltage
Vo = Bus line Output Voltage

Therefore, choose a 4.7KΩ resistor as the value of resistor pull-up