Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 405)

1 Publication AG-UM008C-EN-P - February 2005
Glossary
ACK See Acknowledgment.
Acknowledgment An ASCII control character that indicates the transmission and
acceptance of data.
Asynchronous transmission A method of serial transmission where characters may be
transmitted at unequal time intervals. Asynchronous transmission
requires that each character contains start/stop elements so the
receiver can detect the start and end of each character.
BCC Block-Check Character. The 2’s complement of the 8-bit sum
(modulo-256 arithmetic sum) of all data bytes in a transmission
block. It provides a means of checking the accuracy of each
message transmission.
Bridge An interface between links in a communication network that
routes messages from one link to another when a station on one
link addresses a message to a station on another link.
Classic PLC-5™ Processor A collective name used to refer to PLC-5/10, -5/12, -5/15,
and -5/25 processors.
CRC Cyclic redundancy check. An error detection scheme where all of
the characters in a message are treated as a string of bits
representing a binary number. This number is divided by a
predetermined binary number (a polynomial), and the remainder
is appended to the message as a CRC character. A similar
operation occurs at the receiving end to prove transmission
integrity.
CTS Clear-to-Send. A signal from the modem that tells the transmitting
device to start transmitting data.
DCD Data Carrier Detect. A signal from the modem indicating that the
carrier is being received.
DCE Data Communication Equipment.
1) Equipment that provides the functions required to establish,
maintain, or terminate a connection.
2) The signal conversion and coding required for communication
between data terminal equipment and data circuits. Examples
include modems, line drivers, coaxial cable, satellite links, etc.
DCE may or may not be an integral part of a computer.
DF1 HDx The Allen-Bradley asynchronous half-duplex protocol.
Digital Data Service (DDS) A special wide-bandwidth Private Leased Line (PLL) that uses
digital techniques to transfer data at higher speeds and lower
error rate than voice-band, analog PLLs. The line is available
24 hours a day.