RFID Reader documentation v2.1

ManualsBrandsParallax ManualsBasic Stamp - Educational Boards & KitsRFID reader module

RFID Compatibility

The Parallax RFID Card Reader works exclusively with the EM Microelectronics-Marin SA EM4100-family of

passive read-only transponder tags at 125 kHz. A variety of different tag types and styles exist with the

most popular made available from Parallax. Each transponder tag contains a unique identifier (one of 2

or 1,099,511,627,776 possible combinations) that is read by the RFID Card Reader and transmitted to the

host via a simple serial interface.

Communication Protocol

When the RFID Card Reader is active and a valid RFID transponder tag is placed within range of the

activated reader, the unique ID will be transmitted as a 12-byte printable ASCII string serially to the host

in the following format:

Unique ID

Digit 1

MSB

LSB

Start Byte

(0x0A)

Unique ID

Digit 2

Unique ID

Digit 3

Unique ID

Digit 4

Unique ID

Digit 5

Unique ID

Digit 6

Unique ID

Digit 7

Unique ID

Digit 8

Unique ID

Digit 9

Unique ID

Digit 10

Stop Byte

(0x0D)

The start byte and stop byte are used to easily identify that a correct string has been received from the

reader (they correspond to a line feed and carriage return characters, respectively). The middle ten bytes

are the actual tag's unique ID. For example, for a tag with a valid ID of 0F0184F07A, the following bytes

would be sent: $0A, $30, $46, $30, $31, $38, $34, $46, $30, $37, $41, $0D

All communication is 8 data bits, no parity, 1 stop bit, and least significant bit first (8N1). The baud rate is

configured for 2400 bps, a standard communications speed supported by most any microprocessor or PC,

and cannot be changed. The Parallax RFID Card Reader initiates all communication. Output from the

serial RFID Card Reader TTL level non-inverted. The USB version of the RFID Card Reader handles serial

communications through the VCP (virtual COM port) driver. This allows easy access to the serial data

stream from any programming language that can open a COM port.

Interface Details

The RFID Card Reader is activated via the /ENABLE line. When the RFID Card Reader is powered and the

/ENABLE line is pulled HIGH, the module will be inactive (standby mode) and the LED will be GREEN.

When the /ENABLE line is pulled LOW, the RFID Card Reader enter its active state and enable the

antenna to interrogate for tags. The current consumption of the module will increase dramatically when

the module is active. On the serial version of the RFID Card Reader the /ENABLE line is directly

accessible via the 4-pin header. On the USB version this line is controlled by the COM port DTR line.

Enabling DTR will activate the RFID Card Reader (LED Red) while disabling DTR will deactivate the RFID

Card Reader (LED Green).

A visual indication of the state of the RFID Card Reader is given with the on-board LED. When the

module is successfully powered-up and is in an idle state, the LED will be GREEN. When the module is in

an active state and the antenna is transmitting, the LED will be RED. The LED can be used to visually

indicate to a user that the tag has been read successfully by deactivating the reader briefly when the tag

has been read.

The face of the RFID tag should be held parallel to the front or back face of the antenna (where the

majority of RF energy is focused). If the tag is held sideways (perpendicular to the antenna) you may

have difficulty getting the tag to be read. Only one transponder tag should be held up to the antenna at

any time. The use of multiple tags at one time will cause tag collisions and confuse the reader. The tags

available in the Parallax store have a read distance of approximately 3 inches. Actual distance may vary

slightly depending on the size of the transponder tag and environmental conditions of the application.