Microhard Systems MHX-900, Operating Manual

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MHX-900 Operating Manual: Appendix F
Glossary
can be controlled also by software using X-ON/X-
OFF (transmitter on/off) commands.
Frequency-hopping
A type of spread spectrum
communication whereby the carrier frequency
used between transmitter and receiver changes
repeatedly in a synchronized fashion according to
a specified algorithm or table. This minimizes
unauthorized jamming (interference) and
interception of telecommunications.
Full-duplex
Where data can be transmitted,
simultaneously and independently, bi-
directionally.
Half duplex
Exists when the communications
medium supports bi-directional transmission, but
data can only travel in one direction at the same
time.
Handshaking
A flow-control procedure for
establishing data communications whereby
devices indicate that data is to be sent and await
appropriate signals that allow them to proceed.
Line-of-sight
Condition in which a transmitted
signal can reach its destination by travelling a
straight path, without being absorbed and/or
bounced by objects in its path.
Master
The station which controls and/or polls one
or more Slave stations in a point-to-point or point-
to-multipoint network. Often functions as a server
or hub for the network.
Non-volatile memory
Memory which retains
information which is written to it.
Null modem cable
See Crossover cable .
Point-to-point
A simple communications network
in which only two DTEs are participants.
Point-to-multipoint
A communications network
in which a Master DTE communicates with two or
more Slave DTEs.
Repeater
A device which automatically amplifies
or restores signals to compensate for distortion
and/or attenuation prior to retransmission. A
repeater is typically used to extend the distance
for which data can be reliably transmitted using a
particular medium or communications device.
RS-232
(Recommended Standard 232; more
accurately, RS-232C or EIA/TIA-232E) Defined
by the EIA, a widely known standard electrical
and physical interface for linking DCEs and DTEs
for serial data communications. Traditionally
specifies a 25-pin D-sub connector, although
many newer devices use a compact 9-pin
connector with only the essential signaling lines
used in asynchronous serial communications.
Lines have two possible states: “high” (on, active,
asserted, ca3 to +25 V) or “low” (off,
inactive, disasserted, carrying -3 to -25 V).
RTU
(Remote Terminal Unit) A common term
describing a DTE device which is part of a wide-
area network. Often a RTU performs data I/O and
transmits the data to a centralized station.
Serial communications
A common mode of
data transmission whereby character bits are sent
sequentially, one at a time, using the same
signaling line. Contrast with parallel
communications where all bits of a byte are
transmitted at once, usually requiring a signal line
for each bit.
Shielded cable
Interface medium which is
internally shrouded by a protective sheath to
minimize external electromagnetic interference
(“noise”).
Slave
A station which is controlled and/or polled by
the Master station for communications. Typically
represents one end of a point-to-point connection,
or one of the terminal nodes in a point-to-
multipoint network. Often a RTU is linked by a
Slave DCE.
Spread spectrum
A method of transmitting a
signal over a wider bandwidth (using several
frequencies) than the minimum necessary for the
originally narrowband signal. A number of
techniques are used to achieve spread spectrum
telecommunications, including
frequency hopping .
Spread spectrum provides the possibility of
sharing the same band amongst many users while
increasing the tolerance to interference and noise,
and enhancing privacy of communications.
Throughput
A measure of the rate of data trans-
mission passing through a data communication
system, often expressed as bits or characters per
second (bps or cps).