SMBus FAQ Contents

This page contains answers to common questions about the SBS If and the specifications contained here.  There are answers to questions about specific design topologies along with some tips and tricks that we have found useful and presented here as questions.

How do I join the forum?

Join this forum through the System Management Interface Forum, at the present time.  Click on the link just following this answer.  This link takes you to a download site where you can obtain copies of the Membership Application and an Adopters Agreement.  Download both forms in either PDF or Word format.

Send the completed forms to the address shown at the end of the form.  Send your first year's membership dues with the Forum Membership Application.

Go to the new membership page
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How do I submit comments to the specification?

To comment on the SMBus specification, send mail (click on the link) to: Note that on page ii of the specification is the e-mail address of the SMBus Working Group reflector.  The best way to comment is to send an e-mail to that address.  You may also send comments to me and I will route them to the authors.  Click on this link to send an e-mail to the Webmaster.

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What's new in revision 1.1 of the SMBus specification?



The specification was re-written to clarify many implementation issues and requirements.  Section numbers in revision 1.0 do not correspond to those in revision 1.1. All
The revision 1.1 document is is a stand-alone specification that can be used for SMBus device design independently from the I2C bus. All
Packet Error Checking (PEC) is added to Write Byte, Write Word, Write Block, Read Byte, Read Word and Read Block protocols. If implemented, the protocols insert one byte calculated with a CRC-8 after the last data byte. 7.4, 7.5
Some error recovery methods are described if a transmission error is detected. 7.4, 7.7
AC Electrical Specifications:
No changes exist in the specification between rev 1.0 and rev. 1.1 pertaining to AC electrical specifications.  There is added clarity in the correct use and interpretation of bus timeouts.  There is a sub-section showing alternative bus pull-up methods.
DC Electrical Specifications:
VIL, MAX = 0.8 V  (0.6 V in rev. 1.0)
VIH, MIN = 2.0 V  (1.4 V in rev. 1.0)
ILEAK, MAX = ±5 µA  (±1 µA in rev. 1.0)
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What is the CRC-8 polynomial for SMBus?

The CRC-8 polynomial used in SMBus revision 1.1 is
C(x) = 1 0000 0111.  Refer to the specification for protocol usage.  Click on this link to view a CRC-8 Calculator.

Another handy link and reference to the cyclic redundancy checking for CRC-8 is provided through one of the SBS IF Promoters at

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