System Management Bus (SMBus) Specification Version 3.1 19 Mar 2018 www.powerSIG.org © 2018 System Management Interface Forum, Inc. – All Rights Reserved Filename: SMBus 3_1_20180319.docx Last Saved: 19 March 2018 09:31 System Management Bus (SMBus) Specification Version 3.1 This specification is provided “as is” with no warranties whatsoever, whether express, implied or statutory, including but not limited to any warranty of merchantability, non-infringement or fitness for any particular purpose, or any warranty otherwise arising out of any proposal, specification or sample. In no event will any specification co-owner be liable to any other party for any loss of profits, loss of use, incidental, consequential, indirect or special damages arising out of this specification, whether or not such party had advance notice of the possibility of such damages. Further, no warranty or representation is made or implied relative to freedom from infringement of any third party patents when practicing the specification. Other product and corporate names may be trademarks of other companies and are used only for explanation and to the owner’s benefit, without intent to infringe. Revision No. Date Notes Editor 1.0 15 Feb 1995 General Release Robert Dunstan 1.1 11 Dec 1998 Version 1.1 Release Robert Dunstan 2.0 3 Aug 2000 Version 2.0 Release Robert Dunstan 3.0 20 Dec 2014 Version 3.0 Release Robert V. White Embedded Power Labs 3.1 19 Mar 2018 Version 3.1 Release Robert V. White Embedded Power Labs Questions and comments regarding this For additional information on Smart Battery System specification may be forwarded to: Specifications, visit the SBS Implementer’s Forum [email protected] (SBS-IF) at: www.sbs-forum.org © 2018 System Management Interface Forum, Inc. 2 of 85 All Rights Reserved System Management Bus (SMBus) Specification Version 3.1 Table of Contents 1. Introduction ............................................................................................................................................. 7 1.1 Overview .................................................................................................................................... 7 1.2 Audience .................................................................................................................................... 7 1.3 Scope ......................................................................................................................................... 7 1.4 Organization of this document ................................................................................................... 7 2. Related Documents And Reference Information .................................................................................... 8 2.1 Scope ......................................................................................................................................... 8 2.2 Applicable Documents ............................................................................................................... 8 2.3 Reference Documents ............................................................................................................... 8 2.4 Definitions Of Terms .................................................................................................................. 9 2.5 Conventions ............................................................................................................................. 10 2.5.1 Numeric formats ...................................................................................................... 10 2.5.2 SMBus addresses ................................................................................................... 11 2.5.3 Transaction protocol diagrams ................................................................................ 11 3. General Characteristics ........................................................................................................................ 13 4. Layer 1 – The Physical Layer ............................................................................................................... 14 4.1 Electrical Characteristics Of SMBus Devices – Two Discrete Worlds .................................... 14 4.2 SMBus Common AC specifications ......................................................................................... 15 4.2.1 General timing conditions ........................................................................................ 20 4.2.2 Device timeout definitions and conditions ............................................................... 20 4.2.3 Master device clock extension definitions and conditions....................................... 20 4.2.4 Slave device clock extension .................................................................................. 21 4.2.5 SMBDAT low timeout .............................................................................................. 21 4.3 DC Specifications .................................................................................................................... 21 4.3.1 Supply voltage requirements ................................................................................... 22 4.3.2 SMBus branch circuit model ................................................................................... 22 4.3.3 Low Power DC parameters ........................................................................................ 23 4.3.4 High Power DC specifications ................................................................................. 24 4.3.5 Additional common Low and High Power specifications ......................................... 26 5. Layer 2 – The Data Link Layer ............................................................................................................. 27 5.1 Bit Transfers ............................................................................................................................ 27 5.1.1 Data validity ............................................................................................................. 27 5.1.2 START and STOP conditions ................................................................................. 27 5.1.3 Bus idle condition .................................................................................................... 28 5.2 Data Transfers On SMBus ...................................................................................................... 28 5.3 Clock Generation And Arbitration ............................................................................................ 29 5.3.1 Synchronization ....................................................................................................... 29 5.3.2 Arbitration ................................................................................................................ 30 5.3.3 Clock low extending ................................................................................................ 31 5.4 Data Transfer Formats ............................................................................................................ 33 6. Layer 3 – Network layer ........................................................................................................................ 33 6.1 Usage Model............................................................................................................................ 33 6.1.1 Master devices ........................................................................................................ 33 6.1.2 Slave devices .......................................................................................................... 34 6.1.3 Host ......................................................................................................................... 34 6.2 Device Identification – Slave Address ..................................................................................... 34 © 2018 System Management Interface Forum, Inc. 3 of 85 All Rights Reserved System Management Bus (SMBus) Specification Version 3.1 6.2.1 Uniqueness required ............................................................................................... 34 6.2.2 SMBus address types ............................................................................................. 34 6.3 Using A Device ........................................................................................................................ 36 6.4 Packet Error Checking ............................................................................................................. 36 6.4.1 Packet error checking implementation .................................................................... 36 6.5 Bus Protocols........................................................................................................................... 38 6.5.1 Quick Command ...................................................................................................... 38 6.5.2 Send Byte ................................................................................................................ 38 6.5.3 Receive Byte ........................................................................................................... 39 6.5.4 Write Byte/Word ...................................................................................................... 39 6.5.5 Read Byte/Word ...................................................................................................... 40 6.5.6 Process Call ...........................................................................................................