System Management Bus

SMbus Description

The SMbus is a two wire interface which is based on the I2C bus. The two SMbus lines are called SMBCLK, and SMBDAT and operate at a frequency of 100KHz. Both SMBCLK, and SMBDAT are bidirectional, and pulled high via a resistor [Rp]. Resistor Rs is optional, and used for ESD protection for 'Hot-Swap' devices. VDD may be between 2.7 volts and 5 volts. VIL (Voltage Input Low) is 0.8 volts, and VIH (Voltage Input High) is 2.1 volts. The SMbus link may have multiple Masters and Slaves on the bus, but only one Master may be active at any one time. Slaves may receive or transmit data to the master.

The SMbus is used to communicate between ICs, Temperature Sensors, Smart Battery Charges, and 'Smart' batteries.

Two pins have also been allowed on the PCI bus to support SMbus.
Version 2.0 of SMbus, and an ECR to version 2.2 of the PCI specification added the pins.

SMbus Interface Circuit
System Management Bus Circuit Interconnect

Smart Bus Systems Forum

Definitions and Differences between I2C, Access bus & SMbus; SMSC app note

See PMBus, I2C Bus and AccessBus page
for related information.

SMbus Standards

You can down-load the standard from
System Management Bus (SMBus) Specification Version 2.0 [2000]
Smart Battery Charger Specification Version 1.1
Addition of the SMbus to the PCI Connector ECN to PCI spec 2.2

SMbus Interface IC Manufacturers

Cadex Electronics Inc. {Smart Battery Charges}

Linear Technology {SMBus Programmable CCFL Switching Regulator, Single-Ended 8-Channel/ Differential 4-Channel Analog Multiplexer with SMBus Interface, Micropower, 10-Bit Current Output DAC with SMBus Serial Interface}

Maxim Integrated Products {2-Wire SMBus Temperature Sensors, Li/NiMH/NiCD Battery Charger ICs, Fuel Gauge ICs}

National Semiconductor Corp. {Temperature Sensor Manufacturer}

Texas Instruments Incorporated 'TI'

Xilinx {FPGA Core SMBus Controller ICs}

Larry's Web Page

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Modified 6/13/15
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