Automatic Data Direction Control. An advanced technique for switching a 2-wire RS-485 transmitter on and off. ADDC comes standard with Moxa's serial boards, serial device servers, and other products that transmit serial signals. Detailed configuration information can be found in product user manual.

Asynchronous Communication

Asynchronous communication refers to digital communication (such as between computers) in which there is no timing requirement for transmission, and in which the start of each individual character is signaled by the transmitting device.


Baudrate refers to data transmission speed. For RS-232/422/485 communication, baudrate is measured in bps (bits per second).

COM Port

A COM port is a serial communications port (RS-232 interface) on a computer used to communicate with other devices. It may be a physical port on the back of the computer, through which an external modem or a mouse would connect. External COM (serial) ports has a 9- or 25-pin male connector.

DDNS (Dynamic DNS)

Dynamic DNS is a system that allows the domain name data stored in a domain name server to be updated in real time. The most common use of Dynamic DNS is allowing an Internet domain name to be assigned to a computer that has a dynamic IP address. This makes it possible for other sites on the Internet to establish connections to the machine without needing to track the IP address themselves.


Electronic Chart Display and Information System. A computer-based navigation system that complies with IMO regulations and can be used as an alternative to paper navigation charts. Integrating a variety of real-time information, it is an automated decision aid capable of continuously determining a vessel’s position in relation to land, charted objects, navigation aids and unseen hazards.


Electrostatic Discharge. The sudden release of static electricity when two objects come into contact. Many electronic devices are susceptible to low voltage ESD events. Eg. hard drive components are sensitive to only 10V. One ESD event will not disrupt equipment operation. However, repeated events will degrade equipment's internal components over time.


General Packet Radio Service. GPRS is a packet-oriented mobile data service on the 2G and 3G cellular communication system’s global system for mobile communications (GSM).


Global System for Mobile Communications, originally Groupe Spécial Mobile. GSM is a standard set developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for second generation (2G) digital cellular networks used by mobile phones.


A host is a computer, such as a PC or Linux server, that is connected to a network. Each host is assigned its own unique IP address.


High Speed Packet Access. HSPA is a combination of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that improves the performance of existing 3rd generation mobile telecommunication networks utilizing the W-CDMA protocols. Uplink speed: 5.76 Mbps / Downlink speed: 14.4 Mbps


The Ingress Protection (IP) rating system is used to indicate the type of environment that a piece of electronic equipment can be used in. The first digit (e.g., the “3” in IP30) indicates the ability of the equipment to withstand the ingress of solid objects (including dust), and the second digit (e.g., the “0” in IP30) indicates the ability of the equipment to withstand the ingress of liquids.

   • Protected against solid objects with diameter greater than 2.5 mm.
   • Provides no protection against liquids.

   • Provides complete protection against dust.
   • Protected against low pressure jets of water.

   • Provides complete protection against dust.
   • Protected when immersed in a liquid to a depth of 15 cm to 1 m, for brief periods of time.

   • Provides complete protection against dust.
   • Protected when immersed in a liquid for prolonged periods of time.


Long Term Evolution. LTE is a standard for wireless communication of high-speed data for mobile phones and data terminals. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements.


Mean Time Between Failures. A theoretical value used to indicate the reliability of a product. The MTBF value of a product depends on the known reliability of its various components. It is often expressed in hours.

Optical Isolation

Communication devices connected by long cables may be damaged by the mismatch between ground voltage levels at the two ends of the wire. Optical isolation uses photo cells to isolate the devices' sensitive components from this type of electrical damage.


Power over Ethernet. A technology for wired Ethernet LANs (local area networks) that allows the electrical current necessary for the operation of each device to be carried by the data cables rather than by power cords. Doing so minimizes the number of wires that must be strung in order to install the network. The result is lower cost, less downtime, easier maintenance, and greater installation flexibility than with traditional wiring.


Profinet is an open, real-time, industrial Ethernet standard of profibus & profinet international (PI) for automation.


Remote Authentication Dial In User Service. RADIUS is an AAA (authentication, authorization, and accounting) protocol for controlling access to network resources. RADIUS is commonly used by ISPs and corporations that manage access to Internet or internal networks across an array of access technologies, including modems, DSL, wireless and VPNs.

Asynchronous Communication

Asynchronous communication refers to digital communication (such as between computers) in which there is no timing requirement for transmission, and in which the start of each individual character is signaled by the transmitting device.

Real COM

The Real COM operation mode is used by Moxa's serial device servers to mimick the operation of a serial board. When a serial board is installed in a Windows-based computer, the operating system uses COM numbers (COM1, COM2, etc.) to identify the various serial ports. Real COM mode uses a dedicated driver installed on the computer to apply COM numbers to the serial ports on a serial device server that connects to the computer over a network.


The Restriction on Hazardous Substances (RoHS) directive prohibits the use of lead, cadmium, mercury, hexavalent chromium, Polybrominated Biphenyl (PBB), and Polybrominated Diphenyl Ether (PBDE) flame retardants. RoHS was adopted by the European Union in 2006 and applies to most electronic products marketed in the European Union.


RS-232 is a serial communications standard that provides asynchronous communication capabilities, such as hardware flow control, software flow control and parity check. RS-232 has been widely used for many years. Gears, instruments with digital control interfaces, and communications devices are commonly equipped with serial RS-232 interface. The typical transmission speed of an RS-232 connection is 9600 bps over a maximum distance of 15 meters.


RS-422 is a serial communications standard that provides a longer transmission distance as compared to RS-232. RS-422 uses differential transmission technology to provide transmission speeds of up to 10 Mbps. The maximum transmission distance is 1.2 km at a transmission speed of 9600 bps.


Asynchronous communication refers to digital communication (such as between computers) in which there is no timing requirement for transmission, and in which the start of each individual character is signaled by the transmitting device.

Asynchronous Communication

RS-485 is an enhanced version of RS-422 that also uses a 2-wire bus topology. A 2-wire RS-485 bus can be used to establish an economical network. However, RS-485 only defines electrical signal specifications; users must define the software protocol.

Serial Communication

Serial communication refers to when data is transmitted bit-by-bit, or sequentially, over a single wire.

Serial Device Server

A serial device server is a standalone device that has at least one Ethernet port and one or more serial ports. Serial device servers are equipped with an embedded network operating system and allow computers to access serial devices over a network.


Simple Network Management Protocol. Devices that support SNMP can be configured and managed over the network.


Also referred to as “spikes,” electrical surges are sudden, brief rises in voltage and/or current to a connected load. Standard electrical equipment operating at 120 volts can be damaged by surges of 500 volts or greater.

Surge Protection

A surge protector protects electronic equipment by absorbing excess voltage caused by lightning, electrostatic discharges and other forms of high voltage.


Terminal Access Controller Access-Control System Plus. TACACS+ is a protocol that provides access control for routers, network access servers and other networked computing devices through one or more centralised servers. TACACS+ provides separate authentication, authorisation and accounting services.


Transmission Control Protocol/Internet Protocol. TCP/IP is a set of protocols developed to allow computers to share resources across a network. It was developed by a community of researchers centered around the ARPAnet. The most accurate name for this set of protocols is the "Internet protocol suite." TCP and IP are just two of the protocols in this suite. Because TCP and IP are the best known of the protocols, it has become common to use the term TCP/IP to refer to the entire suite of protocols.

Termination Resistors

When an electrical signal travels through two different resistance junctions in a transmission line, the impedance mismatch will sometimes cause signal reflection. Signal reflection causes signal distortion, which in turn contributes to communication errors. The solution to this problem is to establish the same impedance at the line ends as in the line itself by terminating them with resistors. It is normally sufficient when the value of the termination resistor equals the characteristic impedance of the transmission line. The resistors should be added near the receiving side.


Throughput refers to the performance of data transmission, and is measured by characters actually transmitted or received during a certain period of time. The throughput of a connection depends on CPU, memory, performance between the two devices, pattern of measurement, as well as the performance of the operating system. Throughput is usually measured in bps (bits per second).


Universal Asynchronous Receiver Transmitter. UART chips control the data transmission and reception of a computer's serial communication devices. UART chip converts digital data between parallel data inside the PC and serial data from an RS-232/422/485 line driver.


USB (Universal Serial Bus) is an interface specification designed to allow various peripheral devices to be connected through standardised connectors. USB supports plug-and-play hot swapping. USB 2.0 supports a maximum transfer speed of 480 Mbit/s. USB 3.0 standard was released in 2008 with a maximum transfer speed of 5 Gbit/s. A USB 3.0 port, usually colored blue, is backward compatible with USB 2.0 devices and cables.


Virtual Private Network. A VPN enables a host computer to send and receive data across public networks, such as the Internet, with all the functionality, security and management policies of the private network.

Watchdog Timer

A watchdog timer (WDT) is designed to reboot an operating system automatically if the operating system hangs or crashes. Devices with a WDT can run unattended for long periods of time.



Wireless Fidelity. Wi-Fi is a popular technology that allows an electronic device to exchange data wirelessly (using radio waves) over a computer network, including high-speed Internet connections. The Wi-Fi Alliance (formerly the Wireless Ethernet Compatibility Alliance) started the Wi-Fi (“wireless fidelity”) certification program to test interoperability of 802.11 implementation. This term is sometimes referred to IEEE 802.11 standards-related devices or technologies.


Wireless Local Area Network. A communications network that provides connectivity to wireless devices within a limited geographic area. Today's WLAN are based on IEEE 802.11 standards and are referred as Wi-Fi networks.


Wireless Wide Area Network. A WWAN differs from a wireless local area network (WLAN) by using mobile telecommunication cellular network technologies such as LTE, WiMAX (often called a wireless metropolitan area network or WMAN), UMTS, CDMA2000, GSM, cellular digital packet data (CDPD), and Mobitex to transfer data. It can also use Local Multipoint Distribution Service (LMDS) or Wi-Fi to provide Internet access.


ZigBee technology is based on IEEE 802.15.4 standard to create wireless personal area networks. Zigbee uses low-power digital radios. ZigBee is typically used in low data rate applications requiring long battery life and secure networking.