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Read and write I/O

Read and write the digital and analog I/O of a UR cobot in C# or Python, with RTDE and its masks, or with the Primary Interface.

The I/O of the controller
Which way to choose
Prerequisites
Example
Read a bit
Write with a mask
Troubleshooting
What to read next

This article shows how to read and write the digital and analog I/O of a Universal Robots cobot from a PC, in C# or Python. It compares RTDE, the Primary Interface and URScript, and gives a complete program.

The I/O of the controller

I/O	Numbers	RTDE bits
Standard digital	0 to 7	0 to 7
Configurable digital	0 to 7	8 to 15
Tool digital	0 to 1	16 to 17
Standard analog	0 to 1
Tool analog	0 to 1

Which way to choose

Way	Read	Write	Frequency
RTDE	`ActualDigitalInputBits`, `ActualDigitalOutputBits`, `StandardAnalogInput0`...	`StandardDigitalOutput`, `ConfigurableDigitalOutput`, `StandardAnalogOutput0`..., with a mask	Up to 500 Hz
Primary Interface	`MasterboardData.DigitalInputs`, `DigitalOutputs`, `AnalogInput0`..., `ToolData`	URScript `set_standard_digital_out`... in a secondary program	10 Hz

RTDE is the way for a fast or frequent access. The Primary Interface needs no setup: it is enabled by default.

Prerequisites

The service RTDE (or Primary Client Interface) is enabled on the robot: see Prepare the robot.
To write, the robot is in remote control on e-Series and PolyScope X.
When the robot program also writes an output, decide which side owns it: the last write wins.

Example

The program reads the inputs with RTDE, sets output 2 and resets output 5, then does the same with URScript.

using UnderAutomation.UniversalRobots;
using UnderAutomation.UniversalRobots.Rtde;

class HowToReadWriteIo
{
  static void Main(string[] args)
  {
    
    var robot = new UR();

    var parameters = new ConnectParameters("192.168.0.1");
    parameters.Rtde.Enable = true;
    parameters.Rtde.Frequency = 125;

    // Read: bits 0-7 standard, 8-15 configurable, 16-17 tool
    parameters.Rtde.OutputSetup.Add(RtdeOutputData.ActualDigitalInputBits);
    parameters.Rtde.OutputSetup.Add(RtdeOutputData.ActualDigitalOutputBits);
    parameters.Rtde.OutputSetup.Add(RtdeOutputData.StandardAnalogInput0);

    // Write: a mask selects the outputs, a value sets them
    parameters.Rtde.InputSetup.Add(RtdeInputData.StandardDigitalOutputMask);
    parameters.Rtde.InputSetup.Add(RtdeInputData.StandardDigitalOutput);

    robot.Connect(parameters);
    Thread.Sleep(200);

    // Read the inputs and the outputs
    ulong inputs = robot.Rtde.OutputDataValues.ActualDigitalInputBits;
    bool di3 = (inputs >> 3 & 1) == 1;
    bool configurableDi0 = (inputs >> 8 & 1) == 1;
    double ai0 = robot.Rtde.OutputDataValues.StandardAnalogInput0; // A or V
    Console.WriteLine($"DI3={di3} CI0={configurableDi0} AI0={ai0:F3}");

    // Set DO2 and reset DO5. The other outputs do not change
    var values = new RtdeInputValues();
    values.StandardDigitalOutputMask = (1 << 2) | (1 << 5);
    values.StandardDigitalOutput = 1 << 2;
    robot.Rtde.WriteInputs(values);

    // The same with the Primary Interface, in a secondary program:
    // the running program does not stop
    robot.PrimaryInterface.Script.Send(
      "sec setOutputs():\n" +
      "  set_standard_digital_out(2, True)\n" +
      "  set_standard_digital_out(5, False)\n" +
      "end\n");

    // Read with the Primary Interface, 10 times per second
    bool di0 = robot.PrimaryInterface.MasterboardData.DigitalInputs.Digital0;
    bool toolDi1 = robot.PrimaryInterface.MasterboardData.DigitalInputs.ToolDigital1;

    robot.Disconnect();
    
  }
}

Read a bit

ActualDigitalInputBits holds all the digital inputs in one integer: bit n is (bits >> n) & 1. The masterboard data of the Primary Interface gives each bit as a property: Digital0 to Digital7, Configurable0 to Configurable7, ToolDigital0 and ToolDigital1.

Write with a mask

An RTDE write changes only the outputs of the mask. StandardDigitalOutputMask = 0b0010_0100 selects outputs 2 and 5; StandardDigitalOutput = 0b0000_0100 sets 2 and resets 5. The analog outputs have their own mask, StandardAnalogOutputMask.

Troubleshooting

The output does not change: the robot is not in remote control, or the robot program writes the same output.
The output changes, then goes back: the robot program, or an I/O action of the installation, writes it.
The running program stops: URScript was sent without sec. A line or a def program replaces the running program.

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