Editing System Management Bus (section)

{{Short description|Simple two-wire bus for motherboards}}
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The '''System Management Bus''' ('''SMBus''' or '''SMB''') is a [[single-ended signalling|single-ended]] simple two-wire [[bus (computing)|bus]] for the purpose of lightweight communication. Most commonly it is found in chipsets of computer motherboards for communication with the power source for ON/OFF instructions. The exact functionality and hardware interfaces vary with vendors.

It is derived from [[I²C]] for communication with low-bandwidth devices on a [[motherboard]], especially power related chips such as a laptop's rechargeable battery subsystem (see [[Smart Battery System]] and [[ACPI]]).<ref name="FOLDOC">{{foldoc|System+Management+Bus}}</ref> Other devices might include external master hosts, temperature sensor, fan or voltage sensors, lid switches, clock generator, and [[RGB lighting]]. [[Peripheral Component Interconnect]] (PCI) add-in cards may connect to an SMBus segment.

A device can provide manufacturer information, indicate its model/part number, save its state for a suspend event, report different types of errors, accept control parameters, return status over SMBus, and poll chipset registers. The SMBus is generally not user configurable or accessible.<ref name="FOLDOC" /> Although SMBus devices usually can't identify their functionality, a new [[Power Management Bus|PMBus]] coalition has extended SMBus to include conventions allowing that.

The SMBus was defined by [[Intel]] and [[Duracell]] in 1994.<ref>{{cite web|url=https://www.thefreelibrary.com/DURACELL+AND+INTEL+ANNOUNCE+'SMART+BATTERY'+SPECIFICATIONS+FOR...-a015157559|title=DURACELL AND INTEL ANNOUNCE 'SMART BATTERY' SPECIFICATIONS FOR PORTABLE COMPUTERS - Free Online Library|website=Thefreelibrary.com|access-date=27 October 2017}}</ref> It carries clock, data, and instructions and is based on [[Philips]]' [[I²C]] serial bus protocol.<ref name="FOLDOC" /> Its clock frequency range is 10&nbsp;kHz to 100&nbsp;kHz. (PMBus extends this to 400&nbsp;kHz.) Its voltage levels and timings are more strictly defined than those of I²C, but devices belonging to the two systems are often successfully mixed on the same bus. {{Citation needed|reason=According to whom?|date=March 2017}}

SMBus is used as an interconnect in several platform management standards including: [[Alert Standard Format]] (ASF), [[Desktop and mobile Architecture for System Hardware]] (DASH), [[Intelligent Platform Management Interface]] (IPMI).

SMBus is used to access DRAM configuration information as part of [[serial presence detect]] (SPD). SMBus has grown into a wide variety of system enumeration use cases other than power management.