How to Manage an I²C Device?

Starting release 3.1.3, fischertechnik Robo Pro supports I²C devices and brings new dedicated functions.I²C devices are highly versatile and can be 
  • sensors —a thermometer, 
  • actuators —a LCD display, a stepper controller,
  • or combined —a screen with touch.

The write and read functions required level 4 and are located under the send / receive group.
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Keep in mind:
​Some I²C devices that work with the RoboTX controller may not work or work improperly with the Robotics TXT controller.

Write Function

  • Device address is the unique address of the I²C device, from 0 to 127 or 0x00 to 0x7f. The 0x50 and 0x54 addresses are reserved.
  • Sub-address could be, 8 bits or 16 bits —either MSB=most significant byte first or LSB=least significant byte first.
  • Data could be 8 bits or 16 bits —either MSB=most significant byte first or LSB=least significant byte first.
  • Data value could be either typed-in or imported.
  • Speed is either 100 kHz or 400 kHz. Most I²C devices run at 100 kHz, and some at 400 kHz. Take 100 kHz as default.
  • The error handling offers three option: Repeat until success, Repeat 10 times and Abort immediately. The Repeat 10 times and Abort immediately options add another exit branch to the function in case of an error for error handling.
  • Keep open allows to send more than one byte. If checked, next write function continues sending byte on the flow. This is very handy for sending text to a screen.

For more detailed informations, please refer to chapter 8.2.7 of the Robo Pro help.

Read Function

  • Device address is the unique address of the I²C device, from 0 to 127 or 0x00 to 0x7f. The 0x50 and 0x54 addresses are reserved.
  • Sub-address could be none, 8 bits or 16 bits —either MSB=most significant byte first or LSB=least significant byte first.
  • Data could be 8 bits or 16 bits —either MSB=most significant byte first or LSB=least significant byte first.
  • Data value could be either typed-in or imported.
  • Speed is either 100 kHz or 400 kHz. Most I²C devices run at 100 kHz, and some at 400 kHz. Take 100 kHz as default.
  • The error handling offers three option: Repeat until success, Repeat 10 times and Abort immediately. The Repeat 10 times and Abort immediately options add another exit branch to the function in case of an error for error handling.
  • Keep open allows to send more than one byte. If checked, next read function continues taking byte from the flow. 

For more detailed informations, please refer to chapter 8.2.7 of the Robo Pro help.

Write or Read Mode Than Two Bytes

Let's take the example of the DS1307 real time clock.  Both programs below are identical: 
  • On the left, the address of the register is set for each command
  • On the right, the address of the register is set for the first command only and the sequence is kept open. Note the O for open.
Reading one or two bytes
Reading more than two bytes in a sequence

To read more than 2 bytes, the keep open feature is used. In the case of the DS1307 real time clock, when a register is read, the internal address is incremented by one. So the next read command gets the next value.

Each I²C device has its own registers and commands set, explained in the data-sheet.

First command

Following commands 

Last command
The first command defines the device address and the sub-address. The sub-address may correspond to the address of a register of the device, or to a command for the device.
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  • Keep open is checked. 

This first command opens a read sequence.
In the following commands, there's no need to set the sub-address.

Here, another byte is read.
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  • Keep open is kept checked. 
The only difference with the last command is that keep open is unchecked, and thus closes the read sequence.

  • Keep open is unchecked. 
Sounds complicated? Actually, it is. But there's a plug-and-play solution: the driver.

Operations Cycle

Using an I²C device always relies on the same operations cycle:
  • Initialisation: parameters to set the I²C device.
  • Use: read or / and write operations.
  • End: optionally, at the end.

A driver packs all the functions for a full operation cycle.

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