Definitions

Simplex

This communication method is that the flow of information is always constant in one direction. Information cannot be transferred in reverse direction.

Half Duplex

As one-wire cable is used, this communication method is that information can be transferred in both directions not at the same time, but at regular intervals.

Full Duplex

As two-wire cable is used, this communication method is that data can be sent and received at the same time.

Series sending

This method is to send data bit by bit through one cable. Though baud rate is slow, installation cost is cheap and software is simple.

Parallel sending

This method is used for a video card or a hard disc in a computer and is to transfer data by one byte (8 bits). Though baud rate is fast and data is transferred exactly, there is disadvantage that the longer sending distance is, the higher installation cost is.

Protocol

This is the communication rule prescribed in advance between a sending party and a receiving party to send and receive efficient and confident information without error among more than two (2) computers and terminal units.

Asynchronous method

This method is to send word by word in synchronism in case of series sending. Start bit is sent in front of one character and the character code is sent. Finally, Stop bit is sent.

Node

This is the location where the data in the tree structure of a network is. Each node is composed of the device storing data and the pointer device for sub-node.

BPS and CPS

· BPS : Bits Per Second

· CPS : Characters Per Second

BPS means the number of sending bits in a second. CPS, the abbreviation for characters per second, is the unit of printer speed and means the number of the characters printed by a printer in a second.

Packet

This is a bundle of the data used when sending data. The data communicated between two stations is divided into suitable-size Packets and the packets are sent one by one. Packet includes the information about control such as receiving party, address or control code as well as a certain-size data.

Port

This is the part of the computer used to communicate with other devices. In case of computer link communication, this means RS-232C port or RS-422(485) port.

RS232C

This, one of the communication interface codes established by Electronics Industry Association (EIA), is mainly used to link with diverse devices such as computer, terminal unit, printer, floater and modem. And this is a synchronous series communication interface or an asynchronous series communication interface. There is the disadvantage that sending distance is short and only one to one communication is available, but cost is cheap.

RS422 / RS485

This, one of series communication interfaces such as RS-232C, is used in longer sending distance than the one of RS-232C and one to N access is available. RS-422(1:N) is used for Full Duplex communication with 4 signal lines and RS-485(N:M) is used for Half Duplex communication with 2 signal lines.

BCC

Block Check Character

As series sending may send distorted signal due to the influence of noise to sending line, this is the data that is for a receiving party to decide whether signal is normal or distorted. A receiving party calculates the data received up to the front of BCC and compares the result with received BCC to decide whether signal is normal or not.

FRAME

This, the constant-size data sent in data communication, includes additional information such as destination code, control character for synchronism, parity or CRC to detect an error as well as data.