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SOFTWARE IMPLEMENTATION OF I²C PROTOCOL

by Dariusz Caban

Start ý The Bus ý The Protocol ý The Process ý Conclusions ý Sources and PDF

External devices that are used to expand a microcontrollerýs internal resources are generally available with a parallel interface but a serial interface is becoming more popular. There is a wide range of such devices, including EEPROMs, display controllers, real-time clocks, A/D and D/A converters, and I/O expanders. Serial thermal sensors, directly connectable to a microcontroller, are offered as well. Serially accessed devices require less wiring and space on printed circuit boards than parallel ones. Thus, printed circuit boards and connectors can be simpler and smaller. Reduced wiring also increases reliability of a system. In some cases, such microcontrollers without an external address and data bus, the application of serial devices enables interaction between the microcontroller and the outside world.

Most serial devices are equipped with a synchronous interface for which they require separate signal lines for transferring data and clock information. The clock, called the master, must be supplied by a microcontroller. This clock frequency does not have to be constant. The master also initiates communication with serial devices called slaves. Often, multiple slaves can use common data and clock lines, with each slave having its own select line or address.

One of the most popular synchronous interfaces is the inter-integrated circuit (I²C), which was developed by Philips nearly 20 years ago. I²C is a low-bandwidth, short-distance, two-wire interface that was originally designed to enable communication between devices inside a TV. Now, I²C interface is implemented in over 1000 different devices. [1] Some microcontrollers have a hardware I²C controller built-in (e.g., the P8xC528 from Philips and the PIC16C6x from Microchip). An all-software implementation of I²C protocol is also possible. Thanks to this method, any microcontroller can communicate with I²C devices. In this article, Iýd like to present such an implementation for the popular 8031 microcontroller.

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