Setting General Purpose Outputs with LLRP

This article will cover setting the general purpose outputs through LLRP in C#. First, let's take a look at the simplest example: turning a single GPO on or off. In LLRP, GPOs are controlled through the SET_READER_CONFIG message. The function below creates a SET_READER_CONFIG message, sets the GPO state within that message and then sends the message to the reader.

static void Set_GPO_State(ushort port, bool state)
{
MSG_ERROR_MESSAGE msg_err;
MSG_SET_READER_CONFIG msg = new MSG_SET_READER_CONFIG();
 
// Build the message
msg.GPOWriteData = new PARAM_GPOWriteData[1];
msg.GPOWriteData[0] = new PARAM_GPOWriteData();
msg.GPOWriteData[0].GPOPortNumber = port;
msg.GPOWriteData[0].GPOData = state;
 
// Send the message
MSG_SET_READER_CONFIG_RESPONSE rsp =
reader.SET_READER_CONFIG(msg, out msg_err, 2000);
 
if (rsp != null)
{
// Success
Console.WriteLine(rsp.ToString());
 
}
else if (msg_err != null)
{
// Error
Console.WriteLine(msg_err.ToString());
}
else
{
// Timeout
Console.WriteLine("Timeout Error.");
}
}

Here's an example of how to call the function we just created.

static void Main(string[] args)
{
const ushort GPO_PORT = 1;
const bool GPO_STATE = true;
 
// Create a LLRPClient instance.
reader = new LLRPClient();
 
/*
Connect to the reader.
Replace "SpeedwayR-10-25-32" with your reader's hostname.
The second argument (2000) is a timeout value in milliseconds.
If a connection cannot be established within this timeframe,
the call will fail.
*/
ENUM_ConnectionAttemptStatusType status;
reader.Open("SpeedwayR-10-25-32", 2000, out status);
 
// Check for a connection error
if (status != ENUM_ConnectionAttemptStatusType.Success)
{
// Could not connect to the reader.
// Print out the error
Console.WriteLine(status.ToString());
// Do something here.
// Your application should not continue.
return;
}
 
// Set the GPO state
Set_GPO_State(GPO_PORT, GPO_STATE);
}

Now, let's take the example one step further. Suppose you want to use all four GPO ports to represent a binary word. Some peripheral devices can be controlled this way. A multiplexer, for example, might allow you to select the active antenna by setting a group of inputs to a binary value. Setting the multiplexer control pins to 0011 selects antenna #3, 1001 selects antenna #9, etc. Here's a C# function that takes a number as an input and sets the GPOs to the binary value of that number.

static void Set_GPO_Word(int word)
{
const int NUM_GPO_PORTS = 4;
int i, bitVal;
bool[] bits = new bool[NUM_GPO_PORTS];
 
// Loop through the last four bits in the
// word and store their values in an array
for (i = 0; i < NUM_GPO_PORTS; i++)
{
bitVal = word & 1;
if (bitVal == 1) bits[i] = true;
else bits[i] = false;
word = word >> 1;
}
 
MSG_ERROR_MESSAGE msg_err;
MSG_SET_READER_CONFIG msg = new MSG_SET_READER_CONFIG();
 
// Build the message
msg.GPOWriteData = new PARAM_GPOWriteData[NUM_GPO_PORTS];
for (i = 0; i < NUM_GPO_PORTS; i++)
{
msg.GPOWriteData[i] = new PARAM_GPOWriteData();
msg.GPOWriteData[i].GPOPortNumber = (ushort)(i + 1);
msg.GPOWriteData[i].GPOData = bits[i];
}
 
// Send the message
MSG_SET_READER_CONFIG_RESPONSE rsp =
reader.SET_READER_CONFIG(msg, out msg_err, 2000);
 
if (rsp != null)
{
// Success
Console.WriteLine(rsp.ToString());
 
}
else if (msg_err != null)
{
// Error
Console.WriteLine(msg_err.ToString());
}
else
{
// Timeout
Console.WriteLine("Timeout Error.");
}
}