# Chapter 6: RTDEIOInterface

## About This Chapter

While RTDEControlInterface moves the robot and RTDEReceiveInterface retrieves its state, `RTDEIOInterface` is the I/O operation interface provided by SDU Robotics' `ur_rtde`. It controls the robot's inputs and outputs (I/O) using writable fields of the official Universal Robots RTDE protocol.

It is used to connect external equipment to the robot, including PLC integration, sensor reading, and control of solenoid valves and grippers.

This chapter covers:

- Digital I/O
- Tool I/O
- Analog I/O

---

# 6.1 What Is I/O?

I/O stands for:

```
Input / Output
```

In addition to its motors, a robot must communicate with devices such as:

- Sensors
- Solenoid valves
- Solenoids
- Cylinders
- Grippers
- Lamps
- PLCs

I/O is used to control these devices.

---

# 6.2 Types of I/O

UR robots provide several types of I/O.

| Type | Purpose |
|----|----------------|
| Standard Digital Input | External input |
| Standard Digital Output | External output |
| Tool Digital Input | Input at the tool end |
| Tool Digital Output | Output at the tool end |
| Analog Input | Analog input |
| Analog Output | Analog output |

---

# 6.3 RTDEIOInterface

Creating an instance:

```python
from rtde_io import RTDEIOInterface

rtde_io = RTDEIOInterface(IP)
```

Typically, the following three interfaces are instantiated together:

```python
RTDEControlInterface

RTDEReceiveInterface

RTDEIOInterface
```

---

# 6.4 Standard Digital Output

This is the most frequently used API.

```python
rtde_io.setStandardDigitalOut(pin, value)
```

Example:

```python
rtde_io.setStandardDigitalOut(0, True)
```

This turns DO0 ON.

To turn it OFF:

```python
rtde_io.setStandardDigitalOut(0, False)
```

---

# 6.5 Standard Digital Input

Input states are obtained through `RTDEReceiveInterface`.

```python
state = rtde_r.getDigitalInState(0)
```

The return value is:

```
True

False
```

---

# 6.6 Tool Digital Output

Controls outputs on the tool connector.

```python
rtde_io.setToolDigitalOut(pin, value)
```

Example:

```python
rtde_io.setToolDigitalOut(0, True)
```

This can be used to open or close a robot hand.

---

# 6.7 Tool Digital Input

Inputs at the tool end are also retrieved through the Receive Interface.

Example:

```python
state = rtde_r.getToolDigitalIn(0)
```

*The API name varies depending on the version.*

---

# 6.8 Analog Output

Analog voltage output:

```python
rtde_io.setAnalogOutputVoltage(...)
```

Alternatively, current output:

```python
setAnalogOutputCurrent(...)
```

These can be used for:

- Inverters
- Speed commands
- Voltage commands

---

# 6.9 Analog Input

Analog inputs are obtained through the Receive Interface.

Example:

```python
voltage =
```

Applications include:

- Sensor inputs
- Load cells
- Displacement gauges

---

# 6.10 Gripper Control Example

The simplest sequence is:

```text
OPEN

↓

DO0 ON

↓

Wait 0.5 seconds

↓

DO0 OFF
```

Python:

```python
rtde_io.setStandardDigitalOut(0, True)

time.sleep(0.5)

rtde_io.setStandardDigitalOut(0, False)
```

---

# 6.11 Toggle Operation

Example of blinking an LED:

```python
while True:

    rtde_io.setStandardDigitalOut(0, True)

    time.sleep(0.5)

    rtde_io.setStandardDigitalOut(0, False)

    time.sleep(0.5)
```

---

# 6.12 Combining Motion and I/O

A typical pick operation:

```text
MoveJ

↓

MoveL

↓

Close Gripper

↓

MoveL

↓

MoveJ
```

Code example:

```python
robot.move(...)

robot.move(...)

robot.set_do(0, True)

robot.wait_move()

robot.move(...)
```

---

# 6.13 Waiting for an Input

Waiting for a sensor:

```python
while True:

    if rtde_r.getDigitalInState(0):
        break

    time.sleep(0.01)
```

This can be used for synchronization with a PLC, for example.

---

# 6.14 Precautions for I/O Control

Although I/O updates are relatively fast, they are not suitable for precise timing control within a few milliseconds.

When synchronization with robot position is required, consider combining I/O control with URScript or a Robot Program.

---

# 6.15 Implementation in ur_ctrl.py

In `ur_ctrl.py`, it is recommended to wrap the operations in APIs such as:

```python
set_do()

get_di()

set_tool_do()

get_tool_di()
```

This removes the need for users to interact with `RTDEIOInterface` directly.

---

# Summary

`RTDEIOInterface` handles communication with external devices connected to the robot.

Its main uses are:

- Digital output
- Digital input
- Tool I/O
- Analog I/O

Combining I/O with motion control makes it possible to build practical automated systems.

The next chapter explains the Dashboard Server.