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I2C

I2C will be the most common interface when selecting a microcontroller-level Supported System.

Note that the Daisylink of all connected devices run regardless of the interface used, including I2C. Data is sent and read as a stream, disregarding any I2C start/restart/stop conditions.

Microcomputers​

Many Microcomputers today include a JST connectors that uses I2C bus. Some companies have standards around the same JST connector, such as Sparkfun QWIIC and Adafruit STEMMA products.

A good example is Arduino UNO R4 WiFi. Arduino is one the Supported Systems, providing all the necessary libraries.

Arduino Uno R4 Wifi

Another example is Sparkfun Redboard.

Sparkfun Redboard with DUELink

Many modules on the market include a JST connector with I2C bus signals. They simply use I2C and most will not have any intelligence. DUELink gracefully allows for these modules to be connected on the same daisylink. The only rule is you have to connect the non-DUELink modules first in the chain. Access those module like you normally would, as DUELink will simply ignore them.

QWIIC and STEMMA QT with DUELink modules

tip

You can't use any non-DUELink modules that have the same address as DUELink, which is very unlikely!

The Protocol​

A DUELink module is always listening to a bus master. The I2C device address is 0x52 (7bit), which is fixed and can't be changed.

The host (I2C master) can send data as individual bytes or multiple bytes. The module will look at individual bytes and not how they are packed in individual frames. In other words, start, restart, and stop conditions are not processed by the module.

The device will return 0xFF when the host request data but the device does not have any data to return.

When the device is too busy to accept data, it will use clock stretching feature. Clock stretching support from teh host standard I2C feature and is required from the host.