System Management Bus
The System Management Bus (abbreviated to SMBus SMBus or SMB ) is a two-wire bus that was developed for the modules communication (especially for semiconductor IC ). It helps to recognize the state of components and perform hardware settings. To save power in portable computers (notebook, PDA, phone), it is about better to deactivate unneeded expansion slots or dim the display a bit.
The bit rate on the SMBus is a maximum of 100 kbit / s On each, a SMBus master takes control of the bus (mostly the clock generation ), when communicating with a slave. Communicate two masters together, the Master addressed temporarily takes over the role of a slave.
Since the SMBus usually only two lines ( clock and data line ) is needed, it can be very space-saving laid on boards; also need the connected chips only two pins and fit into smaller housings so.
Since there are slaves which act as controllable switches, so that one can replace jumper (plug-in connecting bridges ) in the main boards. In this way, completely jumper -less motherboard can be realized, allowing the user minimizes manual intervention.
An SMBus device can provide such as manufacturer information, issue the Modell-/Seriennummer, view the status of the power saving mode, report different types of errors, accept control parameters, return a status or control a display. As the use of SMBusses requires detailed knowledge of the present hardware, it is for the user often neither configurable nor accessible. However, on some motherboards it is accessed via a pin header.
The bus was defined by Intel in 1995. The standard specifies the timing of the bus signals and the electrical connection data determined exactly. The SMBus is based on the I ² C- bus protocol from Philips. The voltage level on the bus allowed between 3 V and 5 V in and are therefore backward compatible with those of the I ² C bus.
The SMBus is an optional signal ( Alert # ) that can use the slave to send an interrupt to the controller.
The SMBus support the Microsoft operating systems from Windows 2000, and the open- source operating systems FreeBSD, OpenBSD, NetBSD and Linux.
SMB1 is a common designation for a port of the SM bus.