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RFID Standards Discussion


2009-03-16 10:39:33 AM

Hello Jörgen,

in my opinion and from my experience the reader should always solve a collision.

The "correct" arrangement of your UIDs should be

E0 02 21 9C 52 98 30 3B
E0 02 21 9C 52 98 30 7B

which is just a shifting to MSB first (as described in ISO 15693).

So, the last 4 bits of both UID are the same value and therefore the responses collides in timeslot 10.

Normally, a reader saves the position of collision and tries to solve the collision in the next INVENTORY round.

That means that the mask length will be extended to 4 bits and the mask value will be the time slot of collision (here: 1010 = B). So in the next INVENTORY round the collision can be solved as the two UIDs are different (0011=3 and 0111=7).

For sure, your two UID are a absolutely seldom incidence, as the difference is only 1 bit.

But the collision at the last 4 bits is a common use-case . I had some UID which differs in the 14th LSB bit !

I hope I was able to help you a little bit.
For more details, please feel free to ask !

So long,

> What I want to know is if the ISO 15693 standard should
> solve all collisions between two tags, no matter how equal
> the two tags UIDs are.
> If the answer to this question is yes, then there is a bug
> in my readers firmware.
> The difference between tag 1:s and tag 2:s UIDs are just
> one bit (not a nibble as a wrote earlier).
> I would be very grateful for any reply!!!
> BR,
> Jörgen
> > Hello
> >
> > I'm using a RFID reader from Texas Instruments whichs
> > supports the ISO15693 standard.
> > When reading tags I sometimes get collisions that arn't
> > solved by the reader (i.e. I never get to see the UIDs
> of
> > the coliding tags). Arn't the reader supposed to solve
> all
> > the collisions? I'm only reading two tags at the time.
> > I get the problem when the two tags reply in the same
> > slot.
> >
> > I get the problem when trying to read the following
> tags:
> > UID of tag 1: 3B3098529C2102E0
> > UID of tag 2: 7B3098529C2102E0
> > Are these UIDs too simular? There is just one nibble
> that
> > is changed between them.
> >
> > Is there an error in my reader firmware?
> >
> > The tags I'm using are LRI2K from ST Microelectronics.
> They
> > support anticollision according to their data sheet.
> >
> > I hope that someone has answers to my questions!
> >
> > Best regards,
> > Jörgen

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