51 MCU Series Serial 12 - Serial Bus

Today we will introduce the I2C serial bus. Compared with some of the previous content, this one is relatively difficult to understand. There are many commonly used serial buses, and now we will only briefly talk about the I2C bus.

 

The I2C bus is a serial bus launched by PHLIPS. It is a high-performance serial bus with bus arbitration and high- and low-speed device synchronization functions required by multi-host systems. 

    The I2C bus has only two bidirectional signal lines, one is the data line SDA, and the other is the clock line SCL.

 

   

The I2C bus is connected to the positive power supply through a pull-up resistor. When the bus is idle, both lines are high. A low level output by any device connected to the bus will make the bus signal low, that is, the SDA and SCL of each device are in a line "AND" relationship.

 

   When the I2C bus is transmitting data, the data on the data line must remain stable while the clock signal is at a high level. The high or low level state of the data line is allowed to change only when the signal on the clock line is at a low level.

 

 

When the SCL line is at a high level, the change of the SDA line from a high level to a low level indicates a start signal; when the SCL line is at a high level, the change of the SDA line from a low level to a high level indicates a stop signal.

 

    The start and stop signals are both sent by the host. After the start signal is generated, the bus is in an occupied state; after the stop signal is generated, the bus is in an idle state. If the device connected to the I2C bus has a hardware interface for the I2C bus, it is easy to detect the start and stop signals.

    After receiving a complete data byte, the receiving device may need to complete some other work, such as processing internal interrupt services, and may not be able to receive the next byte immediately. At this time, the receiving device can pull the SCL line to a low level, so that the host is in a waiting state. When the receiving device is ready to receive the next byte, the SCL line is released to a high level, so that data transmission can continue. 

That’s basically it, the most important thing is practice.