Why can't I read my Monza X tag?

"Unpowered" vs. "Powered" Mode Difference

So you're trying to read a Monza X-based tag and it reads fine in "unpowered" mode, but will no longer read once it is placed in "powered" mode.  What's the problem?

Given this situation, the following steps outline what may be going on.

First, make sure you're not making any changes to your reader/antenna configuration or your environment when performing this test.  For example, don't move the tag to a different distance away from the antenna when trying to read the tag in the "unpowered"  versus "powered" state.  The only change that you should make will be to add power to the Monza X-based tag through the DCI pin.  If you're using our Monza X development kit, the "unpowered" state is when the jumper is not engaged on the battery pins and the "powered" state is when the jumper is making a connection between the two pins of the battery.

Steps to perform:

  1. With the Monza X tag in "unpowered" state, place it in front of the reader antenna at a reasonable distance (e.g. 2-3 feet)
  2. Read the tag using Impinj's ItemTest Software
    • Set the reader's search mode to Single Target and Session 0.
  3. You should be able to read the tag
  4. Now, configure the Monza X-based tag for "powered" state
  5. Read the tag using Impinj's ItemTest Software
    • Set the reader's search mode to either Single Target and Session 0.
  6. You should only be able to read the tag once and then the tag will no longer respond to the reader


Why is this doing this?  Is the tag not Gen2 compliant?  Why is the tag behavior different in "powered" state compared to "unpowered" state?

As it turns out, the tag is behaving exactly as it should according to the Gen2 specification.  Since the tag is powered (via DCI pin), then it will have an infinite persistence in session 0. Therefore it will be inventoried once in single target / session 0.  The same is true for sessions 2 and 3. This behavior is consistent with the Gen2 spec.  Powering the tag from I2C (DCI pin) is the same as powering the tag via RF. The Gen2 spec says that session 0 (S0) persistence is “indefinite” when the tag is energized. If the tag is powered via DCI then RF power is not needed and therefore the tag stays in "B" state until you remove the DCI voltage.  This behavior is different than the "unpowered" state because when a reader is sending RF to the tag it is turning  RF power ON/OFF when it hops or changes antennas. Even if it is not hopping (e.g. ETSI reader), the RF is turned ON/OFF on a regular cycle. The tag resets to the "A" state every time that happens and you can then inventory it again. You will get a read every power cycle.  You can verify this is happening by removing the jumper from the battery (or removing power from the DCI pin) and then place the Monza X-based tag back into "powered" state.  If you try to read it after you've done this, you will get one read.

What if this is not the behavior I want?

If you need to read the Monza X-based tag more than once while it is "powered", then you'll need to use a different reader search mode and session.  Try setting the reader to Dual Target or Single Target and Session 1.

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