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Advanced General Purpose Output (GPO) [VIDEO]


Have you ever wanted a way to easily program indicators, such as a stack light, to notify when the Speedway Revolution reader has lost Ethernet connection, is inventorying tags and/or reading tags, or is even functioning (perhaps power unplugged)? How about setting a pulsed duration of the GPO event (i.e. reading and/or encoding tags on a conveyor belt)?

If so, then Advanced GPO functionality is what you are looking for!

You can control the advanced GPO feature of Speedway Revolution readers using this custom parameter.

  • When set to Normal (default) the GPO is set via the regular LLRP SET_READER_CONFIG message.
  • When set to Pulsed, the GPO changes state based on the SET_READER_CONFIG message, and will change to the opposite state after GPOPulseDurationMSec milliseconds. 
  • When set to "Reader_Operational_Status‟, "LLRP_Connection_Status", "Reader_Inventory_Status‟, "Network_Connection_Status‟ or "Reader_Inventory_Tags_Status‟ the GPO status acts like a Boolean value.
  • When high (true, 1), the corresponding status is true, meaning the reader is operating, has a LLRP connection, is inventorying, has a network connection or tags are being singulated (respectively). 
  • When low (false, 0), the opposite is the case.

The following code sample shows how to configure advanced GPO using the LLRP Toolkit (LTK). The method below creates a SET_READER_CONFIG message on the reader that allows for "Reader_Operational_Status‟, "LLRP_Connection_Status", "Reader_Inventory_Status‟, "Network_Connection_Status‟ or "Reader_Inventory_Tags_Status‟ property to be enabled.

Be sure to send the message: msg.AddCustomParameter(GPO) and to do error checking/handling using MSG_SET_READER_CONFIG_RESPONSE.

private void button4_Click(object sender, EventArgs e)
if (btnOpen.Text == "Close")
PARAM_ImpinjAdvancedGPOConfiguration GPO = new PARAM_ImpinjAdvancedGPOConfiguration();
GPO.GPOPortNum = 1;
GPO.GPOMode = new ENUM_ImpinjAdvancedGPOMode();
if (rbNormal.Checked == true)
GPO.GPOMode = ENUM_ImpinjAdvancedGPOMode.Normal;
else if (rbLLRP.Checked == true)
GPO.GPOMode = ENUM_ImpinjAdvancedGPOMode.LLRP_Connection_Status;
else if (rbPulsed.Checked == true)
GPO.GPOMode = ENUM_ImpinjAdvancedGPOMode.Pulsed;
GPO.GPOPulseDurationMSec = 2000;
else if (rbInventory.Checked == true)
GPO.GPOMode = ENUM_ImpinjAdvancedGPOMode.Reader_Inventory_Status;
else if (rbOperatioinal.Checked == true)
GPO.GPOMode = ENUM_ImpinjAdvancedGPOMode.Reader_Operational_Status;
else if (rbITS.Checked == true)
GPO.GPOMode = ENUM_ImpinjAdvancedGPOMode.Reader_Inventory_Tags_Status;
else if (rbNCS.Checked == true)
GPO.GPOMode = ENUM_ImpinjAdvancedGPOMode.Network_Connection_Status;
else MessageBox.Show("Error setting GPO Mode");
MSG_SET_READER_CONFIG_RESPONSE rsp = reader.SET_READER_CONFIG(msg, out msg_err, 12000);
if (rsp != null)
textBox2.Text = rsp.ToString();
else if (msg_err != null)
textBox2.Text = rsp.ToString();
textBox2.Text = "Commmand time out!";
else MessageBox.Show("Please Open Reader and continue");


If you are using Java here is some XML and java code that will pulse GPO 1.  Also, please note that the XML SET_READER_CONFIG portion could be used by C, C#, or C++. 

  • First send the following XML to configure the reader:

<?xml version="1.0"?>
<SET_READER_CONFIG MessageID="0" xmlns:Impinj="http://developer.impinj.com/ltk/schema/encoding/xml/1.18"
<ImpinjAdvancedGPOConfiguration xmlns="http://developer.impinj.com/ltk/schema/encoding/xml/1.18">
  • Use the following java to pulse the GPO 1:
GPOWriteData GPOWriteData = new GPOWriteData();
GPOWriteData.setGPOData(new Bit(true));
GPOWriteData.setGPOPortNumber(new UnsignedShort(1));
msg.setResetToFactoryDefault(new Bit(false)); 
LLRPMessage response = connection.transact(msg, 12000);


Here is a video showing Advanced GPO in action!


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Impinj (NASDAQ: PI) wirelessly connects billions of everyday items such as apparel, medical supplies, and automobile parts to consumer and business applications such as inventory management, patient safety, and asset tracking. The Impinj platform uses RAIN RFID, delivering information about items to the digital world and enabling the Internet of Things.