This guide will go over an example on how to use the a custom command to control an LCD display.

1. getting_started

Any LINX Device.

LINX custom commands allow you to pass a U8 array from LabVIEW to the device which will process the custom data and return a U8 array response.

1. Make sure you're using LINX 1.2 or later.
2. Generate the LINX firmware libraries in the appropriate location for your device's IDE by opening LabVIEW and under the Tools tab go to MakerHub –> LINX –> Generate Firmware Libraries.
3. Generally for MPIDE you want to generate the firmware library in C:\users\*your name*\My Documents\mpide\libraries)
4. Restart the device IDE
5. In the device IDE open the LINX example for the device and interface you're using. (ex. File»Examples»LINX»Arduino_Uno_Serial)
6. The examples are read only so save a copy somewhere. This will be your custom firmware.
7. At the bottom of the firmware, after the void loop, add your custom function. The function must return an int and must have 4 parameters: unsigned char, unsigned char*, unsigned char*, unsigned char*. Below is an example function prototype.
   

 
int myCustomCommand(unsigned char numInputBytes, unsigned char* input, unsigned char* numResponseBytes, unsigned char* response)
{

}

1. numInputBytes is the number of bytes in the input array (from LabVIEW)
2. input is a U8 array which contains the data bytes sent from LabVIEW using the Custom Command VI.
3. numResponseBytes needs to be set to the number of bytes you want to send back to LabVIEW.
4. response is a U8 array. Fill this with the data bytes you want to send back to LabVIEW.
5. The function should return 0 (or use the L_OK constant) if everything went well, or an error number otherwise.
6. The following example custom command increments every byte in the input array by 1 and returns it to LabVIEW

int myCustomCommand(unsigned char numInputBytes, unsigned char* input, unsigned char* numResponseBytes, unsigned char* response)
{
  
  for(int i=0; i<numInputBytes; i++)
  {
    response[i] = input[i] +1;
  }
  
  *numResponseBytes = numInputBytes;
  
  return 0;
}

1. Now the custom command function needs a forward declaration. Above void setup(), add “int myCustomCommand();”
2. Next, custom commands need to be attached to a LINX Listener so they can be called from LabVIEW. This is accomplished using the AttachCustomCommand() function of the LINX Listener.
3. The AttachCustomCommand() takes two arguments:
   1. The first is the custom command number (0-63). This is the number you'll use in LabVIEW to call this command.
   2. The second is the custom function.
4. Add the following code to the setup() function to attach the custom command to the LINX Listener (in this case called LinxSerialConnection)

 LinxSerialConnection.AttachCustomCommand(0, myCustomCommand);

1. Build and deploy/upload the firmware to the device.
2. Use the Custom Command VI (Functions Palette»MakerHub»LINX»Utilities»Custom Command) to call the custom function.
3. Below are the resulting block diagram and front panel for the given code above.

This tutorial describes the process for adding a custom command to a LINX device. It's important to remember that deploying the firmware from the firmware wizard will overwrite the device firmware with the stock version which will not contain your custom commands. If you have any questions about adding customs commands please post on the LINX forums. If you've successfully added a LINX command, consider sharing your work with the community in the forums.

LINX