Rockwell Automation 1747-KE,D17476.12 DH-485/RS-232C Interface Module - Manual (Page 11)

Publication 1747-UM005B-EN-P - March 2006
Preface 3
Half-duplex - a mode of operation for a point-to-point or multi-point
baseband link with two physical circuits, in which messages or
transmission blocks can be sent in one direction or the other, but not
both at the same time.
Modem - Modulator/demodulator. Equipment that connects data
terminal equipment to a communication line.
RAM - random access memory. The type of memory in which each
storage location is by X/Y coordinates, as in core or semiconductor
memory. (Tape or bubble memory cannot be random access.) Thus,
the data access time is independent of the location of the data. Unless
stated otherwise, RAM usually implies read/write and volatile.
RS-232-C - an EIA standard that specifies electrical, mechanical, and
functional characteristics for serial-binary communication circuits in a
point-to-point link.
RS-422 - an EIA standard that specifies electrical characteristics of
balanced-voltage digital interface circuits in a point-to-point link.
RS-423 - an EIA standard that specifies electrical characteristics of
unbalanced voltage digital interface circuits in a point-to-point link.
RS-485 - an EIA standard that specifies mechanical and functional
characteristics for digital interface circuits. This standard is used in
combination with either RS-422 or RS-423.
SLC 500 controller - the SLC 500 family of fixed and modular
controllers.
Conventions Used in This
Manual The following conventions are used throughout this manual.
• Bulleted lists such as this one provide information, not
procedural steps.
• Numbered lists provide sequential steps or hierarchical
information.
• Bold type is used for emphasis