I2C Bus

Contents:

Inter Integrated Circuit bus
Benefits
Features
Examples
Designer benefits
Terminology
Multi-master
Device connection
Bit transfer
START and STOP conditions
Data transfer
Acknowledge
Clock synchronization
Arbitration
A complete data transfer

Inter Integrated Circuit bus

Philips Semiconductors

I2C-BUS SPECIFICATION VERSION 2.1 JANUARY 2000

BENEFITS DESIGNERS AND MANUFACTURERS

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 drivers, remote I/O ports, RAM, EEPROM, or data converters
Application-oriented circuits such as digital tuning and signal processing circuits for radio and video systems, or DTMF generators for telephones with tone dialling.

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 developed a simple bi-directional 2-wire bus for efficient inter-IC control.

This bus is called the Inter IC or I2C-bus.

At present, Philips’ IC range includes more than 150 CMOS and bipolar I2C-bus compatible types for performing functions in all three of the previously mentioned categories.

All I2C-bus compatible devices incorporate an on-chip interface which allows them to communicate directly with each other via the I2C-bus.

This design concept solves the many interfacing problems encountered when designing digital control circuits.

Features

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
A simple master/slave relationships exist at all times;
Masters can operate
- as master-transmitters or
- as master-receivers
It’s 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, bi-directional data transfers can be made at
- up to 100 kbit/s in the Standard-mode,
- up to 400 kbit/s in the Fast-mode, or
- up to 3.4 Mbit/s in the High-speed 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 of 400 pF.

Examples of I2C-bus applications.

TV set

DECT Cordless phone base station

Designer benefits

I2C-bus compatible ICs allow a system design to rapidly progress 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 I2C-bus compatible ICs which 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 I2C-bus interface is already integrated on-chip
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 I2C-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 I2C-bus compatible range offer designers special features which are particularly attractive for portable equipment and battery-backed systems.

They all have: