Inter-integrated circuit (I2C) interface UM0306
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SMBus application usage
With System Management Bus, a device can provide manufacturer information, tell the
system what its model/part number is, save its state for a suspend event, report different
types of errors, accept control parameters, and return its status. SMBus provides a control
bus for system and power management related tasks.
Device identification
Any device that exists on the System Management Bus as a slave has a unique address
called the Slave Address. For the list of reserved slave addresses, refer to the SMBus
specification ver. 2.0 (http://smbus.org/specs/).
Bus protocols
The SMBus specification supports up to 9 bus protocols. For more details of these protocols
and SMBus address types, refer to SMBus specification ver. 2.0 (http://smbus.org/specs/).
These protocols should be implemented by the user software.
Address resolution protocol (ARP)
SMBus slave address conflicts can be resolved by dynamically assigning a new unique
address to each slave device. The Address Resolution Protocol (ARP) has the following
attributes:
● Address assignment uses the standard SMBus physical layer arbitration mechanism
● Assigned addresses remain constant while device power is applied; address retention
through device power loss is also allowed
● No additional SMBus packet overhead is incurred after address assignment. (i.e.
subsequent accesses to assigned slave addresses have the same overhead as
accesses to fixed address devices.)
● Any SMBus master can enumerate the bus
Unique device identifier (UDID)
In order to provide a mechanism to isolate each device for the purpose of address
assignment, each device must implement a unique device identifier (UDID).
For the details on 128 bit UDID and more information on ARP, refer to SMBus specification
ver. 2.0 (http://smbus.org/specs/).
SMBus alert mode
SMBus Alert is an optional signal with an interrupt line for devices that want to trade their
ability to master for a pin. SMBALERT is a wired-AND signal just as the SCL and SDA
signals are. SMBALERT is used in conjunction with the SMBus General Call Address.
Messages invoked with the SMBus are 2 bytes long.
Different address types (reserved, dynamic etc.)
7-bit, 10-bit and general call slave address
types
Different bus protocols (quick command, process
call etc.)
No bus protocols
Table 45. SMBus vs I
2
C
SMBus I
2
C
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