Cyclone® V Hard Processor System Technical Reference Manual

ID 683126
Date 8/28/2023
Public
Document Table of Contents

21.4.3.1. START and STOP Conditions

When the bus is idle, both the SCL and SDA signals are pulled high through pull-up resistors on the bus. When the master wants to start a transmission on the bus, the master issues a START condition. This is defined to be a high-to-low transition of the SDA signal while SCL is 1. When the master wants to terminate the transmission, the master issues a STOP condition. This is defined to be a low-to-high transition of the SDA line while SCL is 1. †

The following figure shows the timing of the START and STOP conditions. When data is being transmitted on the bus, the SDA line must be stable when SCL is 1. †

Figure 109. Timing Diagram for START and STOP Conditions

The signal transitions for the START or STOP condition, as shown in the figure, reflect those observed at the output signals of the master driving the I2C bus. Care should be taken when observing the SDA or SCL signals at the input signals of the slave(s), because unequal line delays may result in an incorrect SDA or SCL timing relationship. †