RFID read write doc

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 via a serial communications interface. The unit

waits in an idle state until it receives a valid header and command from the host, at which time the

module 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.

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 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

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

environmental conditions of the application.

Communication Protocol

The RFID Read/Write Module is controlled by the host via a standard, asynchronous serial

communications interface configured at 9600 bps, 8 data bits, no parity, 1 stop bit, and least significant

bit first (8N1). The serial data expected and transmitted by the RFID Read/Write Module is 5V TTL-level,

non-inverted.

To communicate with 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. A status/error byte and a varying number of

data bytes will be returned depending on the command called.