Specifications

Rockwell Automation Publication AG-SG001G-EN-P - April 2015 79
Glossary
Integrated Service Unit (ISU) Data communication equipment for a digital data network, which serves as the
data transmitting and receiving device. An ISU is a combination of a digital
service unit (DSU) and a channel service unit (CSU).
Link A data channel established between two or more stations.
Logix Controller As part of the ControlLogix System, the Logix controller is a high functionality
device capable of addressing the same requirements as the mid-sized PLC-5
controllers, but with significant functionality for addressing more complex
sequential and process applications. Key benefits include multi-processors within
a chassis, multi-tasking, interrupt-driven controllers, highly integrated motion
control, use of RSLogix 5000 software, improved performance, symbolic
addressing, and controller local/global data scoping
Master Station A device (programmable controller with I/O modules or a workstation) that
sends data to and collects data from devices connected on a point-to-multipoint,
half-duplex network.
Modem A device that modulates digital information from a programmable controller or
computer to an analog signal that is transported over phone lines, radio waves,
and satellite transmissions, and demodulates the analog data back into digital data
at the receiving site.
Modem Handshaking A signaling protocol used for transferring information between devices in a
synchronized manner at a rate acceptable to both devices. It may be accomplished
by hardware or software.
Multidrop Link 1) A link that has more than two stations.
2) Contrasted with point-to-point link.
NAK Negative Acknowledgment. An ASCII control character transmitted by a
receiver as a negative response to the sender.
Node A station on a network.
Octal Numbering System A numbering system that uses only the digits 0...7; also called base-8.
Packet The transmission unit exchanged at the network layer.
Packet Radio Modem An intelligent radio modem that organizes the data it receives from the
transmitting station into packets. The modem places a header and a trailer around
the data before it transmits the data to the destination device. The header can also
contain routing information. Packet radio modems also perform their own data
error checking and will re-transmit the data if an error is encountered.
PAD Packet Assembler/Disassembler. Equipment used to assemble and disassemble
data packets for transmission on a packet-switching network such as a satellite
system.