RFID Reader documentation v2.1

Copyright © Parallax Inc. RFID Card Reader Serial & USB (#28140 / 28340) v2.1 8/28/2008 Page 5 of 11
Interference
The Parallax RFID Card Reader, like many RF devices, may experience RF noise in its frequency range.
This may cause the reader to transmit a spurious tag response when no tag is near the unit. This will not
affect most uses of the RFID Card Reader. To completely prevent spurious responses, it is recommended
to simply read two responses in a row within a given amount of time (e.g. 1 second) to ensure that you
are reading a valid tag and not a “tag” generated by noise.
DC Characteristics
At V
CC
= +5.0V and T
A
= 25ºC unless otherwise noted
Test Specification
Parameter Symbol
Conditions Min. Typ. Max.
Unit
Supply Voltage V
CC
--- 4.5 5.0 5.5 V
Supply Current, Idle I
IDLE
--- --- 10 --- mA
Supply Current, Active I
CC
--- --- 100 --- mA
Input LOW voltage V
IL
+4.5V <= V
CC
<= +5.5V --- --- 0.8 V
Input HIGH voltage V
IH
+4.5V <= V
CC
<= +5.5V 2.0 --- --- V
Output LOW voltage V
OL
V
CC
= +4.5V --- --- 0.6 V
Output HIGH voltage V
OH
V
CC
= +4.5V V
CC
- 0.7 --- --- V
Absolute Maximum Ratings
Condition Value
Operating Temperature -40ºC to +85ºC
Storage Temperature -55ºC to +125ºC
Supply Voltage (V
cc
) +4.5V to +5.5V
Ground Voltage (V
ss
) 0V
Voltage on any pin with respect to V
ss
-0.3V to +7.0V
Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to
the device. This is a stress rating only and functional operation of the device at those or any other
conditions above those indicated in the operation listings of this specification is not implied.
Exposure to maximum rating conditions for extended periods may affect device reliability.
RFID Technology Overview
Material in this section is based on information provided by the RFID Journal (www.rfidjournal.com).
Radio Frequency Identification (RFID) is a generic term for non-contacting technologies that use radio
waves to automatically identify people or objects. There are several methods of identification, but the
most common is to store a unique serial number that identifies a person or object on a microchip that is
attached to an antenna. The combined antenna and microchip are called an "RFID transponder" or "RFID
tag" and work in combination with an "RFID reader" (sometimes called an "RFID interrogator").
An RFID system consists of a reader and one or more tags. The reader's antenna is used to transmit
radio frequency (RF) energy. Depending on the tag type, the energy is "harvested" by the tag's antenna
and used to power up the internal circuitry of the tag. The tag will then modulate the electromagnetic