Voyantic

Reading and Interpreting the EPC Code of an UHF RFID Tag with the Voyantic Tagformance Protocol Testing Tools

Application Note

Published 9/2014
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1 Introduction

This application note discusses the analysis of the EPC code with the Voyantic Tagformance Protocol Testing tool. The paper does not describe other use cases or full functionality of the Protocol Testing Suite, and does not discuss other methods of reading the EPC code or other RFID tag contents.

In addition to the Protocol Testing tools, the EPC code content can be read with the Population Editor tool of the Voyantic Tagformance. Protocol Testing is intended for deeper analysis of the tag performance, such as testing delays and details of code at radio signal level.

2 Verifying the EPC Code Length

The EPC code length written to the tag may vary. In this example a 96bit long EPC code is used as an example.

The EPC code length can be verified with the Voyantic Tagformance Population Editor tool. The Population Editor is a part of the Application Desiger Suite software package, or available as a separate software upgrade (Population support for TDS) with code TF-SW-POS. With the Population Editor it is possible to verify that the EPC of the tag is exactly 96bit. If not, you can use the Editor to write a new 96bit long EPC code.

3 Reading the EPC Code with the Protocol Testing Tool Inventory Command

1. Choose Protocol Testing from the Measurement menu.

2. Press “Start carrier” to start the carrier wave of the reader embedded to the Tagformance system. The Tag state changes from “power off” to “energized” (on the right side of the user interface window).

3. Press “Inventory” for sending the inventory command to the tag. The tag replies to the inventory command and the Tag state changes to “Open” The tag returns data described in picture below.

The reply from the tag can be analyzed with the Voyantic Tagformance

When cursors are placed to “quiet” locations in front and after the tag reply (lower voltage level signal) the signal can be interpreted by pressing the “Interpret” button. The result is shown in the “Interpreted data” window.

Tag reply with the EPC code is the second data string from tag to reader (see picture above).

With 96bits long EPC code the replied data should be 128 bits long; the tag reply includes Protocol Control (PC) bits defining the length of the EPC code, the EPC code (EPC) and the Check bits (CRC16).

PC+EPC+CRC16 (16+96+16=128)

In the example
0011000000000000001100000000010111111011011000111010110000011111
0011100001000001111011001000100000000100011001111111001010011110

When 16 bits from the start and 16 bits from the end are removed, the remaining code is 96bit long EPC code:
0011000000000101111110110110001110101100000111110011100001000001
11101100100010000000010001100111

4 Reading the EPC Code with the Protocol Testing Tool Read Command

1. Choose Protocol Testing from the Measurement menu.

2. Press “Start carrier” to start the carrier wave of the reader embedded to the Tagformance system. The Tag state changes from “Power off” to “Energized” (right side of the user interface window).

3. Press “Inventory” for sending the inventory command to the tag. Tag replies to the inventory command and the Tag state changes to “Open”.

4. When Tag state is open, choose “Read” from the command list and press “Send command” for sending the read command to the tag. Tag replies to the read command. The tag returns data described in picture below.

Again cursors must be placed to quiet locations in front and after the tag answer.

When the data is interpreted, a 161bit long reply is received from the 96bit EPC tag.

Bits are: Header+CRC16+PC+EPC+RN+CRC16 (1+16+16+96+16+16=161)

In this case:
0111100101001111000110000000000000011000000000101111110110110001
1101011000001111100111000010000011110110010001000000001000110011
100001000110111110100011111110101

When 33bits from the start and 32 bits from the end are removed, the remaining code is the 96bit long EPC:
0011000000000101111110110110001110101100000111110011100001000001
11101100100010000000010001100111