Modbus API

Limelight OS features a Modbus TCP server running at (ipaddress):502

• Integers: Integers are SIGNED and encoded using twos complement. This method is universally recognized and ensures correct sign interpretation.

• Floating-Point Numbers: Floats are encoded using the IEEE 754 standard. To comply with the 16-bit register limitation of the Modbus protocol, floating-point numbers are divided into two parts:

  • The higher-order 16 bits are stored in the second register, and the lower-order 16 bits in the first register.
  • Little-endian format ensures compatibility with the Modbus spec.

USB and Ethernet Limelights may be tested with ModbusTool

Modbus enables support for part inspection and industrial automation use-cases. To get started with Modbus, you need to do the following:

1. Connect to your Limelight via Ethernet or USB-C and configure a pipeline.

   • While all pipelines will output results over modbus, our python snapscript pipelines are extremely versatile for industrial use-cases since they support custom input output data.

2. Give your Limelight a static IP address

3. Attach your Limelight to a modbus network.

Modbus Register Specification

Input / Read-Only Registers

Register	Key	Type	Description
0	hb	int	Heartbeat value. Increases once per frame
1	pipelineIndex	int	Current active pipeline index (0 .. 9).
2	validTarget	int	1 if a valid target exists, 0 otherwise.
3	resultsCount	int	Total results count. Includes all fiducial detections, neural detections, etc
4	ID	int	ID / Team Number
5	modbusMode	int	Modbus Server Output Mode.
6	cpuTemp	int	CPU temperature in Celsius.
7	cpuUsage	int	CPU usage percentage.
8	ramUsage	int	RAM usage percentage.
9	currentFPS	int	Current frames per second.
10	captureLatency	int	Capture latency. (milliseconds)
11	targetLatency	int	Processing latency. (milliseconds)
12-15	reserved	int

If Output Mode is set to 0:

Register	Key	Type	Description
16,17	tx	float32	Horizontal angular offset to target in degrees
18,19	ty	float32	Vertical angular offset to target in degrees
20,21	txnc	float32	Horizontal angular offset to target (relative to principal pixel) in degrees
22,23	tync	float32	Vertical angular offset to target (relative to principal pixel) in degrees
24,25	ta	float32 (0-1)	Area of the target as a percentage of the image size
26	fiducialID	int	Current AprilTag ID
27	classifierClass	int	Class Index of current classifier pipeline output. -1 if no Classifier results
28	detectorClass	int	Class Index of current detector pipeline output. -1 if no Detector results
29	reserved	int
30,31	python[0]	float32	Custom python output array [0]
32,33	python[1]	float32	Custom python output array [1]
34,35	python[2]	float32	Custom python output array [2]
36,37	python[3]	float32	Custom python output array [3]
38,39	python[4]	float32	Custom python output array [4]
40,41	python[5]	float32	Custom python output array [5]
42,43	python[6]	float32	Custom python output array [6]
44,45	python[7]	float32	Custom python output array [7]

Holding / Write-Only Registers

Register	Key	Type	Description
0	unlocked	int	Unlocks the pipeline. Set to 1 to enable pipeline switching and custom input data
1	pipeIndex	int	Sets the pipeline index if "unlocked" is set to 1
2	outputMode	int	Sets the output mode. 0 - standard, 1 - rawtargets (WIP)
3	reserved	int
4	reserved	int
5	reserved	int
6	reserved	int
7	reserved	int
8	pythonInput[0]	int	Custom python input array [0]
9	pythonInput[1]	int	Custom python input array [1]
10	pythonInput[2]	int	Custom python input array [2]
11	pythonInput[3]	int	Custom python input array [3]
12	pythonInput[4]	int	Custom python input array [4]
13	pythonInput[5]	int	Custom python input array [5]
14	pythonInput[6]	int	Custom python input array [6]
15	pythonInput[7]	int	Custom python input array [7]
16,17	pythonInput[8]	float32	Custom python input array [8]
18,19	pythonInput[9]	float32	Custom python input array [9]
20,21	pythonInput[10]	float32	Custom python input array [10]
22,23	pythonInput[11]	float32	Custom python input array [11]
24,25	pythonInput[12]	float32	Custom python input array [12]
26,27	pythonInput[13]	float32	Custom python input array [13]
28,29	pythonInput[14]	float32	Custom python input array [14]
30,31	pythonInput[15]	float32	Custom python input array [15]