Data Sheet

Usage

There are many ways to use the RFID Read/Write Module and associated tags, but the three most

common are as follows:

1) Read Only: Read the tag’s unique, non-changing 32-bit serial number

2) Read/Write: Read from and write up to 116 bytes of publicly accessible user data on the tag

3) Read/Write (Protected): Read from and write up to 116 bytes of password-protected user data on

the tag. In this mode, you must enter the correct 32-bit password in order for read and write

operations to be successful.

The RFID Read/Write Module is controlled by the host device. The module waits in an idle state until it

receives a valid header and command, at which time it will perform the command and return a

status/error byte indicating a success or failure and command-specific data (if any). The module will then

re-enter the idle state and wait for the next valid header and command.

If no valid tag is detected within approximately 1.3 seconds after a command is called, the command will

timeout and return the module to an idle state. For the RFID_ReadLegacy command, the timeout is

approximately 0.5 seconds. In the event of a timeout, the module will return an ERR_LIW status byte.

A visual indication of the RFID Read/Write Module’s state is given with the on-board LED (Light Emitting

Diode). 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 (for example, searching for a valid tag or performing an operation

on the tag), the LED will be RED.

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 emitted). If the tag is held sideways (for example, perpendicular to the antenna),

you’ll either get no reading or a poor reading distance. 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 the reader may not

detect any of them. The tags available in the Parallax store have a read distance of approximately 4

inches. Actual distance may vary slightly depending on the size of the transponder tag and environmental

conditions of the application.

Communication Protocol

All communication is 8 data bits, no parity, 1 stop bit, and least significant bit first (8N1) at 9600 bps.

The RFID Read/Write Module Serial version transmits data as 5V TTL-level, non-inverted asynchronous

serial.

The RFID Read/Write Module USB version transmits the data through the host computer’s USB Virtual

COM Port driver. This allows easy access to the serial data stream from any software application,

programming language, or interface that can communicate with a COM port.

To communicate with either version of the RFID Read/Write Module, the user must first send a three-byte

header string of “!RW” (in ASCII), followed by the desired single-byte command (in hexadecimal). Certain

commands require additional data to be sent along with the command. No CR (carriage return) or LF

(linefeed) bytes are required. A status/error byte and a varying number of data bytes will be returned

depending on the command called.