IT2200 Reader System with Multimode Capability Installation & Maintenance/Service Guide
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communicates the initial polling message to the tag. It then transmits an unmodulated
continuous RF wave so that when a tag is within range of the antenna, it can
backscatter its data to the reader. The reader and tag continue this two-way
communications until the transaction has been completed. Normally, at this point, the
reader transmits an encoded acknowledgment (sign-off) message to the tag, and the
tag does not respond to further reader request messages for a programmable period of
time—from 1 to 128 seconds—allowing the vehicle time to travel through the antenna
pattern. During this time-out period, the reader starts communications with the next
tag in the same lane.
In ATA mode, the tags are read-only and do not use a reader-to-tag modulated signal.
When powered, and in the presence of an unmodulated signal, ATA tags always
attempt to backscatter.
Signal Transmission and Acquisition
Amtech® technology uses a single frequency, continuous-wave signal, transmitted
from the reader to the tag, and receives an amplitude modulated form of the same
signal from the tag. This homodyne system uses a sensitive multi-channel
preamplifier to distinguish the return signal from the transmitted signal.
Automatic Vehicle Identification Transaction
Process
Operationally, each tagged vehicle is processed identically whether the toll is
collected on a ticket or barrier system, or the lane is a confined plaza lane or an open,
high-speed express lane. Typical automatic vehicle identification (AVI) operations are
performed as follows:
1. The reader polls for a tag to respond with an identification (ID) number.
2. Once a tag enters the read zone, it responds with its ID number.
3. The reader sends single or multiple requests to the tag to return data or write to
tag memory.
4. At the end of the transaction, the reader sends an acknowledge (ACK) message.
5. The tag goes into a time-out state.
6. The reader polls for the next tag.
If the IT2200 tags respond in ATA mode, the tag identification is read. This completes
the transaction.
Types of RFID Transactions
There are two types of RFID transactions: read-only and read/write. A read-only
transaction is the simplest and consists of a tagged item entering an RF field where the
reader queries the tag’s information. The exchange of information is from the tag to
the reader, no information is returned to the tag.
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