— The bright side of industry automation

Benefits of the I2C Bus

The PWM3 and PWM4 stepper motor cards as well as our custom I/O cards have a built-in I2C bus. This is an industry standard short-range serial bus, using two wires for a data rate of up to 100 kbit/s.

The bus allow several cards to be linked together and controlled from one host computer, using a single RS232 port.

Redundant RS232-ports on the cards can be used for other serial I/O or as failsafe connections for increased reliability.

Embedded systems can also control the cards directly from the I2C bus. The host computer or microcontroller interfaces directly to the bus, with no RS232 hardware or connectors. This allows extremely compact applications.

Robust Design

Our cards, both stepper motor controllers and IO-cards, run in multi-master mode.

This means that if one node should fail or crash, the others can still communicate.

I2C Host OS

Interfacing a control computer or microcontroller directly to the PWM I2C bus is an attractive solution for embedded systems. With no large RS232 serial connectors the overall system can be much smaller.

The bus requires a I2C interface capable of multi-master mode; the computer or controlling processor node must be able to both receive data in slave mode and send in master mode.

Most early Linux kernel implementations can only do I2C communication in master mode, not slave mode.

Some drivers in recent kernels do however support multi-master mode, and can directly be used for interfacing to the I2C bus. We may release sample code demonstrating how to do this soon. Stay tuned!

I2C Addressing

Each device on the I2C bus requires an unique address. Also, the I2C bus requires pull-up resistors.

The address as well as the state of the resistors are set for each card using DIP-switches. (All cards come with the required pull-up resistors, but only one card on the bus can have them enabled.)

When interfacing a host computer to the I2C-bus directly, care must be taken to use a free legal adress.

Learn More

For more information on how to best use I2C in your applications, please contact us.

For more information about addressing and DIP-switch settings, please see the appropriate product datasheet.

Useful information and links

Information about the I2C-bus from NXP

NXP (formerly Philips Semiconductor) invented the I2C bus, used by our PWM and IO cards.