I²C or I2C is a commonly used master-slave based digital communication protocol used by electronic devices.

LabJack T-Series devices are primarily USB and Ethernet data acquisition (DAQ) and control devices. They are designed to be connected to a computer directly with USB or to a local area network (LAN) using their ethernet connection and then controlled by a PC. LabJack's DAQ devices can typically be purchased as OEM (embeddable, without a case or screw terminals) devices. LabJack DAQ Devices page.

This is a web application that I made in about 2018. It is made to prvide a visual to what LabJack T-Series devices output when using their I2C functionality. This web application has typically been able to be found in the LabJack T-Series datasheet in the I2C section.

Please note that this writeup does not apply directly to the U-Series devies.

Additionally, please purchase a logic analyzer before embarking on working with I2C sensors.

That being said, test out various I2C configuration settings and view the expected result.

T-Series I2C Visualizer

I2C Op:

SDA/FIO0:

SCL/FIO0:

Enter I2C Configuration Settings Below

I2C_SDA_DIONUM:

I2C_SCL_DIONUM:

I2C_SPEED_THROTTLE:

I2C_OPTIONS:

Enable Reset-On-Start:
Enable No-Stop on Restart:
Disable Clock Stretching:
Result:

--Input below in hexadecimal--

I2C_SLAVE_ADDRESS:

I2C_NUM_BYTES_TX:

I2C_NUM_BYTES_RX:

I2C_DATA_TX:

I2C_DATA_RX:

Key:

A: Indicates an I2C-Ack bit writing a byte of data
C: Indicates an I2C-Clock stretch occurring to slow down transmission
N: Indicates an I2C-Nack bit writing a byte of data
P: Indicates an I2C-Stop Condition
R: Indicates an I2C-Read bit appearing after the slave address is sent
RESET: Indicates an I2C-Reset Condition
S: Indicates an I2C-Start Condition
W: Indicates an I2C-Write bit appearing after the slave address is sent

T-Series I2C Workflow

The typical work flow for communicating with I2C devices is:

Configure the device using the various configuration registers.

If a I2C write is being performed, write data to the I2C_DATA_TX register.

Write a "1" to the I2C_GO register.

If necessary, read the I2C_NUM_BYTES_RX register to determine how many bytes of data to read from the I2C_DATA_RX register.

Information from support.labjack.com:

The Communications section of the T-Series datasheet describes how you can control and communicate with a T-Series device.

The I2C section of the T-Series datasheet describes all of the device configurations necessary to perform an I2C transaction.

LabJack offers several pre-made Lua Script I2C Examples.

Most LJM Software Example Packages include one or more I2C example, typically using the LJTick-DAC.

Troubleshooting:

Q: Why are no I2C ACK bits being received?

Double check to make sure pull-up resistors are installed. A general rule for selecting the correct size pull-up resistors is to start with 4.7k and adjust down to 1k as necessary. If necessary, an oscilloscope should be used to ensure proper digital signals are present on the SDA and SCL lines.

Double check to make sure the correct I/O lines are being used. It is preferred to do I2C communication on EIO/CIO/MIO lines instead of the FIO lines due to the larger series resistance (ESD protection) implemented on the FIO lines.

Use an oscilloscope to verify the SDA and SCL lines are square waves and not weird arch signals (see "I2C_SPEED_THROTTLE" or use EIO/CIO/MIO lines).

Use a logic analyzer (some oscilloscopes have this functionality) to verify the correct slave address is being used. See this EEVblog post on budget-friendly options. It is common to not take into account 7-bit vs 8-bit slave addresses or properly understand how LabJack handles the defined slave address and the read/write bits defined by the I2C protocol to perform read and write requests.

Make sure your sensor is being properly powered. The VS lines of LJ devices are ~5V and the I/O lines are 3.3V. Sometimes this is a problem. Consider buying a LJTick-LVDigitalIO or powering the sensor with an I/O line or DAC channel.

Q: I've tried everything, still no I2C Ack Bits...

Try slowing down the I2C bus using the "I2C_SPEED_THROTTLE" register/option. Reasons:

Not all I2C sensors can communicate at the full speed of the LabJack. Check the I2C sensor datasheet.
The digital signals could be getting corrupted due to the series resistors of the I/O lines on the LabJack.

Consider finding a way to verify that your sensor is still functioning correctly using an Arduino and that it isn't broken.

Q: Why is my device not being found by the I2C.search function?

See information on I2C ACK bits above.

Q: What are I2C Read and Write functions or procedures?

There are a few really good resources for learning about the general flow of I2C communication.

TI's Understanding the I2C Bus by Jonathan Valdez and Jared Becker is a high quality resource
I2C-bus specification by NXP
Using the I2C Bus by Robot Electronics
I2C Bus Specification by i2c.info

Q: Why am I getting a I2C_BUS_BUSY (LJM Error code 2720) error?

See information on I2C ACK Bits above. Try different pull-up resistor sizes.

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