8.0 LEDs [T-Series Datasheet] | LabJack
« Close

Datasheets and User Guides

App Notes

Software & Driver


8.0 LEDs [T-Series Datasheet]

STATUS - The Green LED

The status LED indicates when the T-series device is performing autonomous tasks, such as running an on-board Lua script or streaming. The LED will blink when a Lua script accesses a Modbus register or when a stream packet is prepared.

The status LED also activates during firmware updates to indicate various stages of the process, refer to the Combined LED Activity section.

COMM - The Yellow LED

The primary indicator for packet transfer.  If the T-series device is communicating the COMM LED will be blinking.  A few blinks after connecting to the PC indicates that the T-series device is enumerating.  Enumeration is when the standard USB initialization takes place and the host is gathering device information.  

The COMM LED will blink when the T-series device receives Modbus commands, or when streaming data.  Each packet will produce a single blink.  If commands are issued rapidly, the LED will blink rapidly.  At high packet transfer rates the LED will blink at 10Hz, even if more than 10 packets are being processed per second.

Normal Behavior

Here are 3 examples of normal LED behavior.  For troubleshooting it is useful to compare these examples to what you see on your device.


  1. Both LEDs blink rapidly for about 1 second.
  2. COMM solid off and STATUS solid on.
  3. If USB enumerates, COMM blinks a few times and then stays solid on.


Both LEDs solid on.  No blinking

While Viewing Kipling's Dashboard

Green LED solid on.  Orange LED also solid on but with a quick double-blink once per second.


If LED behavior is not normal, please see USB Communication Failure.

Combined LED Activity

When the LEDs blink together, the T4/T7 is computing checksums.

When the LEDs are alternating, the T4/T7 is copying a firmware image.

LED Configuration

The LED mode can be set using the following registers:

Name Start Address Type Access

POWER_LED             Sets the LED operation:<br>0 = Off. Useful for lower power applications.<br>1 = normal.<br>2 = Lower power, LEDs will still blink but will normally be off.<br>3 = Reserved.<br>4 = Manual, in this mode the LEDs can be user controlled.

48006 UINT16 R/W

POWER_LED_DEFAULT             The ON/OFF state of the LEDs after a power-cycle to the device.

48056 UINT16 R/W

When POWER_LED is set to manual mode, the LEDs can be turned on and off using the following registers:

Name Start Address Type Access

LED_COMM             Sets the state of the COMM LED when the LEDs are set to manual, see the POWER_LED register.

2990 UINT16 W

LED_STATUS             Sets the state of the STATUS LED when the LEDs are set to manual, see the POWER_LED register.

2991 UINT16 W