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RM0091 Inter-integrated circuit (I

C) interface

Doc ID 018940 Rev 1 501/742

23.4.11 SMBus specific features

This section is relevant only when SMBus feature is supported. Please refer to Table 23.3:

I2C implementation.

Introduction

The System Management Bus (SMBus) is a two-wire interface through which various

devices can communicate with each other and with the rest of the system. It is based on I2C

principles of operation. SMBus provides a control bus for system and power management

related tasks.

This peripheral is compatible with the SMBUS specification rev 2.0

(http://smbus.org/specs/).

The System Management Bus Specification refers to three types of devices.

● A slave is a device that receives or responds to a command.

● A master is a device that issues commands, generates the clocks and terminates the

transfer.

● A host is a specialized master that provides the main interface to the system’s CPU. A

host must be a master-slave and must support the SMBus host notify protocol. Only

one host is allowed in a system.

This peripheral can be configured as master or slave device, and also as a host.

SMBUS is based on I2C specification rev 2.1.

Bus protocols

There are eleven possible command protocols for any given device. A device may use any

or all of the eleven protocols to communicate. The protocols are Quick Command, Send

Byte, Receive Byte, Write Byte, Write Word, Read Byte, Read Word, Process Call, Block

Read, Block Write and Block Write-Block Read Process Call. These protocols should be

implemented by the user software.

For more details of these protocols, refer to SMBus specification ver. 2.0

(http://smbus.org/specs/).

Address resolution protocol (ARP)

SMBus slave address conflicts can be resolved by dynamically assigning a new unique

address to each slave device. 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). This 128-bit number is implemented by software.

This peripheral supports the Address Resolution Protocol (ARP). The SMBus Device

Default Address (0b1100 001) is enabled by setting SMBDEN bit is I2Cx_CR1 register. The

ARP commands should be implemented by the user software.

Arbitration is also performed in slave mode for ARP support.

For more details of the SMBus Address Resolution Protocol, refer to SMBus specification

ver. 2.0 (http://smbus.org/specs/).

STMicroelectronics STM32F05 series User Manual

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