282
The
VIC
20
User
Guide
Terminology
The following
is
a list of common terms used in telecommunications:
Modem
The peripheral device used to convert the signals output by
your computer into information that can be transmitted over the
telephone lines. ("Modem" stands for "modulate/ demodulate.")
Handshaking The process
of
sending data and waiting for
an
acknowl-
edgement from the receiving computer.
Full/
half
duplex These are two modes
of
handshaking.
In
full duplex
mode, a computer sends some
data
and the receiving computer
repeats the
data
back
to
the originating computer.
If
the data
returned are the same as those sent, the originating computer
sends the next byte.
If
they are incorrect, the data are sent again.
In half duplex mode, the originating computer sends data and the
receiving computer simply acknowledges that the data have been
received.
Baud rate This indicates the maximum speed
at
which data are trans-
mitted and received. The VIC Modem sends and receives data
at
300 baud. Another way
of
describing baud rate
is
in BPS, or bits
per second. A system running
at
300 baud will send/receive
300
bits
of
data per second.
Answer / originate When you connect
to
one
of
the networks, you will
be calling the system. Since you are originating the call, your
modem should
be
set to "originate." This sets up the "introduc-
tory" protocol in the electronics.
If
you are communicating
directly with another computer, one computer must be in origi-
nate mode and the other
in
answer mode. Once communications
have been established, it makes no difference which
is
which.
Parity In order
to
verify that the
data
transmitted are correct, some
computers will send
an
extra bit called the parity bit along with
the data.
If
the total of all the "ON" (or I) bits, including the parity
bit,
is
an even number, the transmission
is
odd parity.
If
the parity
bit
is
missing, the transmission has no parity. To communicate
properly, both computers must be set to the same parity.
Word length This
is
the number
of
bits in each byte. Most computers
use a word length of seven
or
eight bits.
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