Information processing equipment used for communications
is
called data terminal equipment (DTE). Equipment used to connect
the
DTE
to the communications line
is
called
data
communications
equipment (DCE).
An
adapter
is
used
to
connect the
data
terminal equipment
to
the
data communications line as shown in the following illustration:
Data
Data
Communications
Terminal
Communications
Line
Equipment
Equipment
Z
Voice
Line
EIA/CCITT
Cable
Conforming
to
EIA
Modem
Adapter
or
CCITT
Standards
Clock
The
EIAI
CCITT adapter allows
data
terminal equipment
to
be
connected
to
data
communications equipment using
EIA
or
CCITT
standardized connections.
An
external modem
is
shown in this
example; however, other types
of
data
communications equipment
can also be connected
to
data
terminal equipment using
EIA
or
CCITT standardized connections.
EIA
standards are labeled RS-x (Recommended Standards-x) and
CCITT standards are labeled V.x or X.x, where x
is
the number
of
the standard.
The
EIA
RS-232 interface standard defines the connector type, pin
numbers, line names,
and
signal levels used
to
connect
data
terminal equipment
to
data
communications equipment for the
purpose
of
transmitting and receiving data. Since the RS-232
standard was developed, it has been revised three times. The three
revised standards are the RS-232A, the RS-232B, and the presently
used RS-232C.
The CCITT V.24 interface standard
is
equivalent to the RS-232C
standard; therefore, the descriptions
of
the
EIA
standards also
apply
to
the CCITT standards.
Communications
8-3
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