Writing an RFID tag with Direct Protocol

I recently had to send a customer a Direct Protocol sample that wrote to an RFID tag and printed a bar code. The sample in the manual didn’t work, but this one does:

INPUT ON

REM BAR CODE
PP168,204:AN7
BARSET “CODE39”,8,3,1,102
PB “1234567890”

REM HUMAN READABLE
PP244,113:NASC 8
FT “Univers”
FONTSIZE 24
FONTSLANT 0
PT “1234567890”

REM RFID
TAGFIELD “@ID”,4,10
TAGFORMAT “ASCII”
TAGWRITE “1234567890”

PF

Send this to an RFID equipped PM43 and a bar code with human readable text will print, and an RFID tag will be written with the same values.

Will RFID make all of my dreams come true?

People unfamiliar with RFID technology expect to walk into a room, turn on an RFID reader and read all of the tag inside of the room. It doesn’t work that way.

RFID is a great data collection tool but you should be familiar with its basic operation. Our industry mostly uses passive UHF tags that operate in the 900 MHz frequency. Here’s a typical RFID inlay, or circuit:

The little black dot in the middle of the inlay is the RFID chip, the rest is the antenna. This is a passive tag which means that it does not use a battery, the tag gathers energy from radio waves aimed at it. Electromagnetic waves are made up of two waves, one electrical and one magnetic. When the magnetic part of the wave cuts across the antenna an electrical current is induced, which charges up the RFID chip. When enough energy is stored the RFID chip can begin to communicate. It does this by powering the antenna on and off, which reflects the incoming radio wave (on) or lets it pass through (off). Rapidly turning the antenna on and off is how the RFID chip modulates the reflected signal, which is how data is sent back to an RFID reader.

So there’s a couple of important things to note from this. First, the RFID inlay does not transmit radio signals, it reflects them, so the power coming back to the reader is quite small. People think that RFID tags work like the transponders in their cars that are used to collect toll information. These are active tags that have in internal battery and really do create and transmit radio waves (transmitter/responder) and have much greater range than passive RFID.

Secondly, the RFID circuit gathers energy from the magnetic part of the radio wave aimed at it, and sometimes the tag’s antenna can be orientated to that this doesn’t happen and the tag can’t be read. Radio waves can be blocked, absorbed, or reflected, by nearby materials, preventing the tag from being powered up or read. There are a lot of things that can go wrong.

RFID is a great technology, but it should be approached with caution. Always test your RFID tags in the environment where they will be used with the readers and antennas that you have chosen to make sure your application will be robust and reliable.