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Byte A group of bits, typically 8 bits, operated on as a single unit. A single ASCII character typically occupies one byte. (See Octet).
Carrier Sense In a Local Area Network, an ongoing activity of a network node to detect whether another node is transmitting.
Carrier Sense Multiple Access with Collision Detection (CSMA/CD) A bus network in which the medium access control protocol requires carrier sense and in which exception conditions caused by collision are resolved by retransmission.
Channel A channel is an abstract term used to describe a connection between a client Series 90 PLC and a server Series 90 PLC and the periodic transfer of data between the two devices.
Channel Status Bits The Channel Status bits comprise bits
Client A node that requests network services from a server. A client PLC initiates a communications request. (See also Server.)
Collision A condition that results from concurrent transmissions by two or more nodes on the transmission medium.
Collision Domain A single CSMA/CD network. If two or more nodes are within the same collision domain and both transmit at the same time, a collision will occur. Nodes separated by a repeater are within the same collision domain. Nodes separated by a bridge are within different collision domains.
Command Dictionary Provides an alphabetical listing of the LAN Interface commands.
Command Field That part of a protocol data unit (PDU) that contains commands, as opposed to the address field and information field.
COMMREQ Function Block The COMMREQ Function Block is the Series 90 PLC ladder instruction used to initiate a communications request.
COMMREQ Status Word The
Communications Window A part of the PLC scan that provides an opportunity for the LAN Interface to read and write PLC memory. The window is executed automatically once per PLC scan.
Connection A logical communication link established between two end points and used to transfer information.
CRS Word See COMMREQ Status Word.
CSMA/CD See Carrier Sense Multiple Access with Collision Detection.
DCS Words See Detailed Channel Status Words.
Detailed Channel Status Words Two status words containing detailed information on a single Series 90 channel. The DCS words are retrieved using the Retrieve Detailed Channel Status Command.
Appendix A Glossary |