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Basic Read/Write Tutorial

This section provides examples of how to write code in Python to read and write data to DYNAMIXEL motors.

NOTE: This tutorial is based on XL-430-W250 DYNAMIXEL motors and uses Protocol 2.0.

Make python file

Create a python file and open it in a text editor. In this case, we use visual studio code, but you can use any text editor you prefer.
```
$ mkdir -p my_dxl_project/python
$ cd my_dxl_project/python
$ code my_read_write.py
```

Make python file

Open the Visual Studio Code and create a python file in your workspace.

Source Code Description

Add Header Files

Add #!/usr/bin/env python3 and import dynamixel_sdk to the top of your py file. This includes all necessary functions and classes from the DYNAMIXEL SDK.
```
#!/usr/bin/env python3

from dynamixel_sdk import *
```

Initialize Handler Objects

Initialize the PortHandler and PacketHandler. Set the port name and protocol version according to your DYNAMIXEL setup. The example below uses /dev/ttyUSB0 as the port name and 2.0 as the protocol version.
```
portHandler = PortHandler("/dev/ttyUSB0")  # your dxl port name
packetHandler = PacketHandler(2.0)  # protocol version
```

Initialize the PortHandler and PacketHandler. Set the port name and protocol version according to your DYNAMIXEL setup. The example below uses COM3 as the port name and 2.0 as the protocol version.
```
portHandler = PortHandler("COM3")  # your dxl port name
packetHandler = PacketHandler(2.0)  # protocol version
```

Open Port and Set Baud Rate

Open the port and set the baud rate. The example below uses 57600 as the baud rate.
```
portHandler.openPort()
portHandler.setBaudRate(57600)
```

ERROR LOGGING

openPort() and setBaudRate() functions return a boolean value indicating success or failure. If you want to check for failure, you can write like below to print an error message and exit the program.

if portHandler.openPort():
  print("Succeeded to open the port!")
else:
  print("Failed to open the port!")
  exit()

if portHandler.setBaudRate(57600):
  print("Succeeded to change the baudrate!")
else:
  print("Failed to change the baudrate!")
  exit()

Write data to enable torque

Turn on the torque of the DYNAMIXEL.
```
dxl_id = 1
torque_on_address = 64
data = 1
packetHandler.write1ByteTxRx(portHandler, dxl_id, torque_on_address, data)
```
- id : Dynamixel ID you set
- address : The address of the data you want to write. Refer to the Control Table of your DYNAMIXEL model, which can be found in its specification manual or Dynamixel Wizard 2.0. In this example, we use X series.
- data : The data you want to write to the specified address.

ERROR LOGGING

write1ByteTxRx() returns a communication result. If you want to check the communication result and error, you can write the code as shown below.

dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, dxl_id, torque_on_address, data)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))
else:
    print("Dynamixel has been successfully connected")

Get User Input

Get user input for the target position.

while True:
    try:
        target_position = int(input("Enter target position (0 ~ 4095, -1 to exit): "))
    except ValueError:
        print("Please enter an integer.")
        continue

    if target_position == -1:
        break
    elif target_position < 0 or target_position > 4095:
        print("Position must be between 0 and 4095.")
        continue

Write data to set target position

Write the target position to the DYNAMIXEL.

    goal_position_address = 116
    packetHandler.write4ByteTxRx(portHandler, dxl_id, goal_position_address, target_position)

ERROR LOGGING

write4ByteTxRx() returns a communication result. If you want to check the communication result and error, you can write the code as shown below.

    dxl_comm_result, dxl_error = packetHandler.write4ByteTxRx(portHandler, dxl_id, goal_position_address, target_position)
    if dxl_comm_result != COMM_SUCCESS:
        print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
    elif dxl_error != 0:
        print("%s" % packetHandler.getRxPacketError(dxl_error))

Read data from DYNAMIXEL

Read the current position from the DYNAMIXEL.

    while True:
        present_position_address = 132
        present_position, dxl_comm_result, dxl_error = packetHandler.read4ByteTxRx(portHandler, dxl_id, present_position_address)
        print(f"Current Position: {present_position}")

        if abs(target_position - present_position) <= 10:
            break

ERROR LOGGING

read4ByteTxRx() returns a communication result. If you want to check the communication result and error, you can write the code as shown below.

        present_position, dxl_comm_result, dxl_error = packetHandler.read4ByteTxRx(portHandler, dxl_id, present_position_address)
        if dxl_comm_result != COMM_SUCCESS:
            print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
        elif dxl_error != 0:
            print("%s" % packetHandler.getRxPacketError(dxl_error))

Turn off the torque when while loop is exited. And close the port.

data = 0
packetHandler.write1ByteTxRx(portHandler, dxl_id, torque_on_address, data)
portHandler.closePort()

Run the Code

Run the code using python3.
```
$ python3 my_read_write.py
```

Run the code through Visual Studio Code.

Full Source Code

#!/usr/bin/env python3

from dynamixel_sdk import *


portHandler = PortHandler("/dev/ttyUSB0")
packetHandler = PacketHandler(2.0)

if portHandler.openPort():
  print("Succeeded to open the port!")
else:
  print("Failed to open the port!")
  exit()

if portHandler.setBaudRate(57600):
  print("Succeeded to change the baudrate!")
else:
  print("Failed to change the baudrate!")
  exit()

dxl_id = 1
torque_on_address = 64
data = 1
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, dxl_id, torque_on_address, data)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))
else:
    print("Dynamixel has been successfully connected")

while True:
    try:
        target_position = int(input("Enter target position (0 ~ 4095, -1 to exit): "))
    except ValueError:
        print("Please enter an integer.")
        continue

    if target_position == -1:
        break
    elif target_position < 0 or target_position > 4095:
        print("Position must be between 0 and 4095.")
        continue

    goal_position_address = 116
    dxl_comm_result, dxl_error = packetHandler.write4ByteTxRx(portHandler, dxl_id, goal_position_address, target_position)
    if dxl_comm_result != COMM_SUCCESS:
        print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
    elif dxl_error != 0:
        print("%s" % packetHandler.getRxPacketError(dxl_error))

    while True:
        present_position_address = 132
        present_position, dxl_comm_result, dxl_error = packetHandler.read4ByteTxRx(portHandler, dxl_id, present_position_address)
        if dxl_comm_result != COMM_SUCCESS:
            print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
        elif dxl_error != 0:
            print("%s" % packetHandler.getRxPacketError(dxl_error))
        print(f"Current Position: {present_position}")

        if abs(target_position - present_position) <= 10:
            break

data = 0
packetHandler.write1ByteTxRx(portHandler, dxl_id, torque_on_address, data)
portHandler.closePort()

#!/usr/bin/env python3

from dynamixel_sdk import *


portHandler = PortHandler("COM3")
packetHandler = PacketHandler(2.0)

if portHandler.openPort():
  print("Succeeded to open the port!")
else:
  print("Failed to open the port!")
  exit()

if portHandler.setBaudRate(57600):
  print("Succeeded to change the baudrate!")
else:
  print("Failed to change the baudrate!")
  exit()

dxl_id = 1
torque_on_address = 64
data = 1
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, dxl_id, torque_on_address, data)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))
else:
    print("Dynamixel has been successfully connected")

while True:
    try:
        target_position = int(input("Enter target position (0 ~ 4095, -1 to exit): "))
    except ValueError:
        print("Please enter an integer.")
        continue

    if target_position == -1:
        break
    elif target_position < 0 or target_position > 4095:
        print("Position must be between 0 and 4095.")
        continue

    goal_position_address = 116
    dxl_comm_result, dxl_error = packetHandler.write4ByteTxRx(portHandler, dxl_id, goal_position_address, target_position)
    if dxl_comm_result != COMM_SUCCESS:
        print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
    elif dxl_error != 0:
        print("%s" % packetHandler.getRxPacketError(dxl_error))

    while True:
        present_position_address = 132
        present_position, dxl_comm_result, dxl_error = packetHandler.read4ByteTxRx(portHandler, dxl_id, present_position_address)
        if dxl_comm_result != COMM_SUCCESS:
            print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
        elif dxl_error != 0:
            print("%s" % packetHandler.getRxPacketError(dxl_error))
        print(f"Current Position: {present_position}")

        if abs(target_position - present_position) <= 10:
            break

data = 0
packetHandler.write1ByteTxRx(portHandler, dxl_id, torque_on_address, data)
portHandler.closePort()