Serial Communication Glossary
| Baudrate |
| Baud rate indicates the transmission speed on the serial line. With RS232/422/485 interfaces, the baudrate is the same as the transfer rate in bps. |
| Bit |
| Binary digit, can have value 0 or 1 |
| Bitrate |
| The bitrate defines the number of bits transmitted in a specified amount of time |
| Carrier Detect |
| Carrier detect, signal line on the DCE to indicate the presence of a carrier signal. |
| Clear To Send |
| Clear To Send, signal line on the DCE to handshake with the DTE. |
| Control Characters |
| ASCII codes which are used for special functions in serial communications. |
| Data Communication Equipment |
| Examples of Data Communication Equipment are modems, faxes and GSM modems. |
| Data Set Ready |
| Data Set Ready, signal line on the DCE to handshake with the DTE. |
| Data Terminal Equipment |
| Examples of Data Terminal Equipment are computers, printers, terminals and PDA's. |
| Data Terminal Ready |
| Data Terminal Ready, signal line on the DTE to handshake with the DCE. |
| Databits |
| The number of bits that are used to send a single character over a serial line. |
| EIA-561 |
| Standard for using a modular connector (RJ45) for asynchronous serial communications. |
| Electronic Industries Alliance |
| Electronic Industries Alliance is a standardization organization that defines and maintains all kinds of electronics standards. |
| First In First Out |
| FIFO is a buffer where the data is retrieved from in the same order as it was added during recption |
| Flow Control |
| Flow control is used to regulate the dataflow between a DTE and DCE to ensure that no buffer overflow and thus no loss of data is caused. There are two sorts of flowcontrol, hardware and software flow control. |
| Handshaking |
| Handshaking is used to regulate the dataflow between a DTE and DCE to ensure that no buffer overflow and thus no loss of data is caused. There are two sorts of flowcontrol, hardware and software flow control. |
| Mark |
| Transmission of a binary '1'. On a serial line this is a negative voltage (for RS232: -3 to -12 volts). |
| Modem |
| Modem is the abbreviation of Modulator Demodulator. A modem is used to convert Digital to Analog signals to be transmitted over a telephone line. |
| Parity bit |
| A bit at the end of every character which is used for error detection. This bit is computed from the databits. |
| Public Services Telephone Network |
| Your fixed telephone line |
| Request To Send |
| Request To Send, signal line on the DTE to handshake with the DCE. |
| RS232 |
| RS-232 is a long-established standard that describes the physical interface and protocol for low-speed serial data communication between devices. This is the interface that e.g. a computer uses to talk to and exchange data with a modem and other serial devices. |
| RS422 |
| RS-422 is a serial data communication protocol that specifies 4-wire, full-duplex, differential line, multi-drop communications. It provides balanced data transmission with unidirectional/non-reversible, terminated or non-terminated transmission lines. RS-422 does not allow multiple drivers, only multiple receivers. Maximum recommended range is 4,000 feet (1200 meters). Maximum recommended baud rate is 10Mbit/s. |
| RS485 |
| RS-485 is an upgraded version of RS-422 that supports up to 32 devices on the same connection. RS-485 is an electrical specification of a two-wire, half-duplex, multipoint serial connection. It enables the configuration of inexpensive local networks and multidrop communications links. It offers high data transmission speeds (up to 10Mbit/s), and as it uses a differential balanced line over twisted pair (like RS-422), it can span relatively large distances (4000 feet or 1200 meters). RS-485 only specifies the electrical characteristics of the driver and the receiver. It does not specify or recommend any data protocol. |
| Serial Communications |
| Communications over a single wire, where only one bit is transmitted at a time |
| Space |
| Transmission of a binary '0'. On a serial line this is a positive voltage (for RS232: +3 to +12 volts).. |
| Start bit |
| A bit that indicates the start of a new character on the serial line. |
| Stop bit |
| A bit that indicates the end of a character on the serial line. |
| Synchronous communications |
| Normally the clock signals are extracted from the start and stopbits. When using synchronous communications, a clock signal is used to indicate the start and end of every byte. An USART is needed to use synchronous communications. |
| Universal Asynchronous Receiver Transmitter |
| The chip used to control the data in serial communication devices. UART's are used in RS232/485 and 422 devices. |
| Universal Synchronous/Asynchronous Receiver Transmitter |
| Same as an UART, but it also supports synchronous communications. |
| V24 |
| European name for RS232 |
| V25 |
| Standard for communication with a modem, also called Hayes AT command protocol. |
| XON/XOFF |
| Software handshaking by using XON and XOFF control characters. |