SMBus overview

SMBus (system management bus) is the abbreviation of system management bus. The bus is proposed and maintained by sbs-if (sbs-if, smartbattery system implementers Forum), which is initiated by Intel. SMBus bus is mainly used in the communication between intelligent battery and MCU, low speed communication between PC system and system sensor, etc.

SMBus Interface Signal

SMBus is a subset of I2C protocol (commonly used digital interface (3) I2C). The mapping relationship between SMBus Interface signal and I2C signal is as follows, in which SMBus #, smbalert #, are optional signals, and the protocol is not mandatory.


Table 1 SMBus Interface Signals

SMBus application block diagram

Same as I2C.

SMBus frame format

SMBus protocol frame is defined based on the common frame format defined by I2C.


Figure 1 SMBus frame format

As shown in Figure 1, the first byte of the frame format defined by SMBus protocol is the same as that of I2C protocol, transmitting slave address and read-write command. Starting from the second byte, different frames are formed by specifying the content of data. For example, filling the data1 with the command code to indicate a specific operation (the protocol does not describe the command code in detail), filling the end byte of the frame with the PEC (CRC-8 check) to enhance the reliability of transmission, etc. For details, please refer to Chapter 5 of the protocol.

The difference between SMBus and I2C

In Appendix B, SMBus protocol details the differences between SMBus and I2C. The summary is as follows


Table 2 differences between MBus and I2C

The differences between SMBus and I2C are mainly reflected in four aspects: electrical characteristics, timing, ACK usage and frame format. Generally, it supports I2C digital IP and SMBus through mode configuration.

Editor in charge: CC

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