Rockwell Automation 2755 AtomScan Bar Code Reader - Manual (Page 139)

Glossary G–4
Publication 2755-6.9
Relay Driver – A TTL signal sent by the reader. The output is
determined by the relay driver selection (by operational command).
ROM – Read Only Memory. Memory that cannot be changed.
RS-232 – RS-232 defines an interface between two devices such as
the reader and host. It differs from the other interfaces by dedicating
individual pins to specific functions and by requiring both devices to
share a common ground line (pin 4). Since both device chassis are
connected to a common ground, a ground loop potential and the
possibility of noise interference exists. Therefore, cable lengths are
limited to a maximum of 50 feet (19.7 m). Despite being the most
limited, this interface is used frequently because of the large installed
base of RS-232 equipment
.
RS-422 – RS-422, unlike RS-232, measures signals differentially.
The receiver looks at the potentials between the two receive (or
transmit) wires rather than the potential between signal and ground.
As a result, cables, if shielded, can be up to 4000 ft (1219 m) in
length. Like RS-232, RS-422 communication is designed for only
two devices on a single line. It can be used wherever RS-232 is
used.
RS-485 – RS-485, like RS-422, can transmit up to 4000 ft (1219 m)
using differential voltages but unlike RS-422, RS-485 transmitters
are turned off until a request for data is received from the host.
RS-485 is used exclusively in multidrop protocol.
Scan Rate – Number of scans per second that the reader projects.
Scan Width – That portion of the scan line in which a label can be
read.
Serial Commands – Online data strings (including configuration
and operations) from a host or other terminal to the reader, that are
always preceded by a < left angle bracket symbol and followed by a
> right angle bracket symbol.
Sinking/Sourcing – Describes a current signal flow relationship
between field input and output devices in a control system and their
power supply. A sourcing interface box supplies current (source) to
a sinking field device (e.g., package detect).
Skew – Label (or reader) rotation around the center of the skew axis.
Spicular Reflection – The direct, mirror-like reflection of laser light
back to the reader, causing over-light saturation.