UM10204
I
2
C-bus specification and user manual
Rev. 6 — 4 April 2014
User manual
Document information
Info
Keywords
Abstract
Content
I2C, I2C-bus, Standard-mode, Fast-mode, Fast-mode Plus, Fm+,
Ultra Fast-mode, UFm, High Speed, Hs, inter-IC, SDA, SCL, USDA, USCL
Philips Semiconductors (now NXP Semiconductors) developed a simple
bidirectional 2-wire bus for efficient inter-IC control. This bus is called the
Inter-IC or I
2
C-bus. Only two bus lines are required: a serial data line
(SDA) and a serial clock line (SCL). Serial, 8-bit oriented, bidirectional
data transfers can be made at up to 100 kbit/s in the Standard-mode, up to
400 kbit/s in the Fast-mode, up to 1 Mbit/s in the Fast-mode Plus (Fm+), or
up to 3.4 Mbit/s in the High-speed mode. The Ultra Fast-mode is a
uni-directional mode with data transfers of up to 5 Mbit/s.
NXP Semiconductors
UM10204
I
2
C-bus specification and user manual
Revision history
Rev
v.6
Date
20140404
Description
User manual; sixth release
Modifications:
•
•
Figure 41 “R
p(max)
as a function of bus capacitance”
updated (recalculated)
Figure 42 “R
p(min)
as a function of V
DD
”
updated (recalculated)
v.5
v.4
v.3
20121009
20120213
20070619
User manual; fifth release
User manual Rev. 4
Many of today’s applications require longer buses and/or faster speeds. Fast-mode Plus was
introduced to meet this need by increasing drive strength by as much as 10× and increasing the
data rate to 1 Mbit/s while maintaining downward compatibility to Fast-mode and Standard-mode
speeds and software commands.
Version 2.1 of the I
2
C-bus specification
The I
2
C-bus has become a de facto world standard that is now implemented in over 1000 different
ICs and licensed to more than 50 companies. Many of today’s applications, however, require higher
bus speeds and lower supply voltages. This updated version of the I
2
C-bus specification meets those
requirements.
Version 1.0 of the I
2
C-bus specification
first release
v2.1
v2.0
2000
1998
v1.0
Original
1992
1982
Contact information
For more information, please visit:
http://www.nxp.com
For sales office addresses, please send an email to:
salesaddresses@nxp.com
UM10204
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2014. All rights reserved.
User manual
Rev. 6 — 4 April 2014
2 of 64
NXP Semiconductors
UM10204
I
2
C-bus specification and user manual
1. Introduction
The I
2
C-bus is a de facto world standard that is now implemented in over 1000 different
ICs manufactured by more than 50 companies. Additionally, the versatile I
2
C-bus is used
in various control architectures such as System Management Bus (SMBus), Power
Management Bus (PMBus), Intelligent Platform Management Interface (IPMI), Display
Data Channel (DDC) and Advanced Telecom Computing Architecture (ATCA).
This document assists device and system designers to understand how the I
2
C-bus works
and implement a working application. Various operating modes are described. It contains
a comprehensive introduction to the I
2
C-bus data transfer, handshaking and bus
arbitration schemes. Detailed sections cover the timing and electrical specifications for the
I
2
C-bus in each of its operating modes.
Designers of I
2
C-compatible chips should use this document as a reference and ensure
that new devices meet all limits specified in this document. Designers of systems that
include I
2
C devices should review this document and also refer to individual component
data sheets.
2. I
2
C-bus features
In consumer electronics, telecommunications and industrial electronics, there are often
many similarities between seemingly unrelated designs. For example, nearly every
system includes:
•
Some intelligent control, usually a single-chip microcontroller
•
General-purpose circuits like LCD and LED drivers, remote I/O ports, RAM,
EEPROM, real-time clocks or A/D and D/A converters
•
Application-oriented circuits such as digital tuning and signal processing circuits for
radio and video systems, temperature sensors, and smart cards
To exploit these similarities to the benefit of both systems designers and equipment
manufacturers, as well as to maximize hardware efficiency and circuit simplicity, Philips
Semiconductors (now NXP Semiconductors) developed a simple bidirectional 2-wire bus
for efficient inter-IC control. This bus is called the Inter IC or I
2
C-bus. All I
2
C-bus
compatible devices incorporate an on-chip interface which allows them to communicate
directly with each other via the I
2
C-bus. This design concept solves the many interfacing
problems encountered when designing digital control circuits.
Here are some of the features of the I
2
C-bus:
•
Only two bus lines are required; a serial data line (SDA) and a serial clock line (SCL).
•
Each device connected to the bus is software addressable by a unique address and
simple master/slave relationships exist at all times; masters can operate as
master-transmitters or as master-receivers.
•
It is a true multi-master bus including collision detection and arbitration to prevent data
corruption if two or more masters simultaneously initiate data transfer.
•
Serial, 8-bit oriented, bidirectional data transfers can be made at up to 100 kbit/s in
the Standard-mode, up to 400 kbit/s in the Fast-mode, up to 1 Mbit/s in Fast-mode
Plus, or up to 3.4 Mbit/s in the High-speed mode.
UM10204
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© NXP Semiconductors N.V. 2014. All rights reserved.
User manual
Rev. 6 — 4 April 2014
3 of 64
NXP Semiconductors
UM10204
I
2
C-bus specification and user manual
•
Serial, 8-bit oriented, unidirectional data transfers up to 5 Mbit/s in Ultra Fast-mode
•
On-chip filtering rejects spikes on the bus data line to preserve data integrity.
•
The number of ICs that can be connected to the same bus is limited only by a
maximum bus capacitance. More capacitance may be allowed under some
conditions. Refer to
Section 7.2.
Figure 1
shows an example of I
2
C-bus applications.
I
2
C
A/D or D/A
Converters
V
DD4
I
2
C
General Purpose
I/O Expanders
I
2
C
LED Controllers
I
2
C
DIP Switches
I
2
C
Slave
V
DD5
I
2
C
Repeaters/
Hubs/Extenders
V
DD0
V
DD2
I
2
C Port
via HW or
Bit Banging
V
DD1
I
2
C
Bus Controllers
8
MCUs
I
2
C
Multiplexers
and Switches
PCA9541
I
2
C
Master Selector/
Demux
MCUs
I
2
C
Serial EEPROMs
LCD Drivers
(with I
2
C)
I
2
C
Real Time Clock/
Calendars
I
2
C
Temperature
Sensors
V
DD3
Bridges
(with I
2
C)
SPI
UART
USB
002aac858
Fig 1.
Example of I
2
C-bus applications
2.1 Designer benefits
I
2
C-bus compatible ICs allow a system design to progress rapidly directly from a
functional block diagram to a prototype. Moreover, since they ‘clip’ directly onto the
I
2
C-bus without any additional external interfacing, they allow a prototype system to be
modified or upgraded simply by ‘clipping’ or ‘unclipping’ ICs to or from the bus.
Here are some of the features of I
2
C-bus compatible ICs that are particularly attractive to
designers:
•
Functional blocks on the block diagram correspond with the actual ICs; designs
proceed rapidly from block diagram to final schematic.
•
No need to design bus interfaces because the I
2
C-bus interface is already integrated
on-chip.
UM10204
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© NXP Semiconductors N.V. 2014. All rights reserved.
User manual
Rev. 6 — 4 April 2014
4 of 64
NXP Semiconductors
UM10204
I
2
C-bus specification and user manual
•
Integrated addressing and data-transfer protocol allow systems to be completely
software-defined.
•
The same IC types can often be used in many different applications.
•
Design-time reduces as designers quickly become familiar with the frequently used
functional blocks represented by I
2
C-bus compatible ICs.
•
ICs can be added to or removed from a system without affecting any other circuits on
the bus.
•
Fault diagnosis and debugging are simple; malfunctions can be immediately traced.
•
Software development time can be reduced by assembling a library of reusable
software modules.
In addition to these advantages, the CMOS ICs in the I
2
C-bus compatible range offer
designers special features which are particularly attractive for portable equipment and
battery-backed systems.
They all have:
•
•
•
•
Extremely low current consumption
High noise immunity
Wide supply voltage range
Wide operating temperature range.
2.2 Manufacturer benefits
I
2
C-bus compatible ICs not only assist designers, they also give a wide range of benefits
to equipment manufacturers because:
•
The simple 2-wire serial I
2
C-bus minimizes interconnections so ICs have fewer pins
and there are not so many PCB tracks; result — smaller and less expensive PCBs.
•
The completely integrated I
2
C-bus protocol eliminates the need for address decoders
and other ‘glue logic’.
•
The multi-master capability of the I
2
C-bus allows rapid testing and alignment of
end-user equipment via external connections to an assembly line.
•
The availability of I
2
C-bus compatible ICs in various leadless packages reduces
space requirements even more.
These are just some of the benefits. In addition, I
2
C-bus compatible ICs increase system
design flexibility by allowing simple construction of equipment variants and easy
upgrading to keep designs up-to-date. In this way, an entire family of equipment can be
developed around a basic model. Upgrades for new equipment, or enhanced-feature
models (that is, extended memory, remote control, etc.) can then be produced simply by
clipping the appropriate ICs onto the bus. If a larger ROM is needed, it is simply a matter
of selecting a microcontroller with a larger ROM from our comprehensive range. As new
ICs supersede older ones, it is easy to add new features to equipment or to increase its
performance by simply unclipping the outdated IC from the bus and clipping on its
successor.
UM10204
All information provided in this document is subject to legal disclaimers.
© NXP Semiconductors N.V. 2014. All rights reserved.
User manual
Rev. 6 — 4 April 2014
5 of 64
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