SMBUS和i2cBus,PMBus 区别

SMBus	I2C
最大传输速度 100kHz	最大传输速度400kHz
最小传输速度 10kHz	无最小传输速度
35ms时钟低超时	无时钟超时
固定的逻辑电平	逻辑电平由VDD决定
不同的地址类型（保留、动态等） 7位、 10位和广播呼叫从地址类型	不同的总线协议（快速命令、 处理呼叫等) 无总线协议

 http://www.i2c-bus.org/

The System Management Bus (SMBus) is more or less a derivative of the I2C bus. The standard has been developed by Intel and is now maintained by the SBS Forum.

The main application of the SMBus is to monitor critical parameters on PC motherboards and in embedded systems. For example there a lot of supply voltage monitor, temperature monitor, and fan monitor/control ICs with a SMBus interface available.

There are some interesting differences between the I2C bus and the SMBus:

• Packet Error Checking (PEC)
• Timeout for transfers
• Standardized transfer types
• ALERT line
• SUSPEND line
• Power down/up
• max. bitrate of 100 kHz/s

Just like the I2C-Bus, the SMBus defines a protocol for inter-device communication. It adds timeouts and standards for data transfer formats, however it does not define the content of transmitted data.

The new PMBus? standard is based on the SMBus. It defines a set of commands and data structures required by power control and management components.

This allows interoperability between ICs not only on the electrical level, but also regarding the command semantics.

As an example, the PMBus defines a command for setting and reading over voltage level - something that is essencial in the power management domain.

In this sense, the PMBus is not a new bus but a protocol layer on top of the SM-Bus.

More information about the PMBus can be found at www.pmbus.com

The PMBus name and logo are trademarks of SMIF, Inc.