Radio Frequency Identification
A method of reading a card using radio frequency energy to transmit information from the card to a reader. See Proximity.

Random Access Memory (RAM)
Randomly addressable, readable and writable memory (either volatile or nonvolatile) whose contents may be read or be altered at will.

Reader
A device that "receives" an identification code from a card, key tag, magnetic stripe card, bar code card, or related item.

Relay
A device that is capable of opening a normally-closed circuit or closing a normally-open circuit. When the relay is not energized, the normally-closed circuit is complete and the normally-open circuit is open. When the relay is energized, it switches roles, opening the normally-closed circuit and closing the normally-open circuit. This dual nature of a relay allows for two types of applications: a device may be attached to the normally-closed circuit so that the device is always on until the relay energizes to turn it off, or a device may be attached to the normally-open circuit so that the device is always off until the relay energizes to turn it on.

Request to Exit (RTE)
A signal that informs the controller that someone has requested to exit from a secure area.

REX
An acronym for Request to Exit. See Request to Exit.

Read Only Memory (ROM)
Nonvolatile memory whose contents are programmed into the ROM when the ROM is made, and therefore cannot be altered. ROM is typically used to store programs and fixed data sets.

Real Time Command
A command that is executed immediately, with no time delay.

RFID
See Radio Frequency Identification.

ROM
See Read Only Memory.

RS-232
A serial communication protocol used for connecting data terminal devices. RS-232 is the most commonly used communication protocol.

RS-485
A serial communication protocol used for multi-drop communication applications. It is used for higher speed and longer distance communications.

RTE
See Request to Exit.