ALLEN BRADLEY 1747-L551 PLC Processor

GL–4
Glossary
Network — A series of stations (nodes) connected by some type of
communication medium. A network may be made up of a single
link or multiple links.
Node — Also called a station. An address or software location on
the network.
Nominal Input Current — The current at nominal input voltage.
Off-State Current — For input circuits, the maximum amount of
leakage current allowed from an input device in its Off-state.
Off-State Leakage — For output circuits, the maximum amount of
(leakage) current that may flow when the output circuit is in its
Off-state.
Off-State Voltage (max) — The maximum input voltage level
detected as an Off condition by the input module.
On-State Voltage Drop — The voltage developed across the output
driver circuit during the On state at maximum load current.
Operating Voltage — For inputs, the voltage range needed for the
input to be in the On state. For outputs, the allowable range of
user-supplied voltage.
Output Device — A device, such as a pilot light or a motor starter
coil, that is energized by the programmable controller.
Points per Common — The number of input or output points
connected to a single return (common) or supply (vcc).
Poll Message — A poll message is a point-to-point transfer of data
sent by the scanner that solicits a response from a single device. The
device responds with its data bit and status bit.
Protocol — The “language” or packaging of information that is
transmitted across a network.
(I/O) Rack — An I/O addressing unit that corresponds to 8 input
image-table words and 8 output image-table words. A rack can
contain a maximum of 8 I/O groups for up to 128 discrete I/O.
Remote I/O Network — A network where the communication
between the processor and the I/O is across a serial link.
RS-232 — An EIA standard that specifies electrical, mechanical,
and functional characteristics for serial binary communication
circuits. A single-ended serial communication interface.
RTB —Removable Terminal Block.
Publication 1747-6.2