Multitech MMH900 User Manual page 188

DTMF (Dual-Tone MultiFrequency): A
generic push-button concept made popular by
AT&T TouchTone.
Decibel (dB): A unit of measurement for
signal strength based on logarithmic incre-
ments. A decibel is a relative measurement
that is derived from an initial reference level
and a final observed level.
Default: This is preset value or option in
software packages, or in hardware configura-
tion, that is used unless you specify
otherwise.
Device driver: Software that controls how a
computer communicates with a device, such
as a printer or mouse.
Digital signal: Digital devices, such as
terminals and computers, transmit data as a
series of electrical pulses which have discrete
jumps rather than gradual changes.
Digital Transmission: A method of
electronic information transmission common
between computers and other digital devices.
Analog signals are waveforms: a combination
of many possible voltages. A computer's
digital signal may be only "high" or "low" at
any given time. Therefore, digital signals may
be "cleaned up" (noise and distortion
removed) and amplified during transmission.
DIP switch (pronounced "dip switch"): A
set of tiny toggle switches, built into a DIP
(dual in-line package), used for setting
configurable parameters on a PCB (printed
circuit board).
DPSK (Differential Phase Shift Keying): A
common form of phase modulation used in
modems. It does not require complex
demodulation circuitry and is not susceptible
to random phase changes in the transmitted
waveform, thus reducing errors during
transmission.
DSR (Data Set Ready): An RS232 signal
sent from the modem to the computer or
terminal indicating that it is able to accept
data. Contrast with DTR.
DTR (Data Terminal Ready): An RS232
signal sent from the computer or terminal to
the modem indicating that it is able to accept
data.
E
EBCDIC (Extended Binary Coded Decimal
Interexchange Code) (pronounced "eb suh
dick"): An IBM character code used in its
mainframe and midrange computers. It is an
8-bit code (256 combinations) that stores one
alphanumeric character or two decimal digits
within a byte. This code and ASCII are the
most commonly used to represent data.
Echo: The reflection or duplication of a signal
back toward its source. Echoing is useful
when a terminal is transmitting data, in that
the data can be echoed to the screen so the
user can monitor what is being sent. Echoing
is undesirable when it refers to the signal
which results on a telephone line from
impedance mismatches.
Echo cancellation: A high speed modem
technique that isolates and filters out
unwanted signals caused by echoes from the
main transmitted signal. This allows full-
duplex modems to send and receive on the
same frequency carrier.
EIA (Electronics Industries Association):
A membership organization founded in 1924
that includes manufacturers of electronic parts
and systems. With over 1200 members, it
sponsors shows and seminars and gives
awards for outstanding contributions in
electronics. It sets electronic interface
standards, such as RS-232.
Environment: A computer configuration that
includes the CPU model and system software
(operating system, data communications and
database systems). It may also include the
programming language used. It sets the
standards for the applications that run in it.
EPROM (Erasable Programmable Read
Only Memory) (pronounced "eeprom"): A
reusable PROM chip that holds its contents
until erased under ultraviolet light.
Error correction: The process of detecting
distorted data bits and requesting a retrans-
mission or interpretation to correct the error.
Errors are introduced by bad line conditions or
external interface.
F
Fax (facsimile): Refers to the bit-mapped
rendition of a graphics-oriented document
(fax) or to the electronic transmission of the
image over telephone lines (faxing). Fax
transmission differs from data transmission in
that the former is a bit-mapped approximation