User`s guide
9
Communications
This
terminal
is
equipped
with
three
communications
ports.
The
two
serial
ports
are
intended
for
connection
to
either
a
host
(or
modem),
an
alternate
input
device
such
as
a
scanner,
or a
serial
printer.
(The EIA
port
has
both
an
RJ45
and
a
DB25
interface;
either,
but
not
both,
can
be
used.)
The
last
port
is
a
Centronics-compatible
printer
port
which
could
be
used
with
a
parallel
printer
or
other
output
device
(such
as
a
cash
drawer)
connected
to a
parallel
interface.
The
port
you
use
as
the
printer
port
depends
on
whether
you
have
a
serial
or a
parallel
interface
to
the
printer.
Another
factor
affecting
your
port
selection
is
whether
the
terminal
is
being
used
in
a
single
or
dual
host
environment.
Either
"EIA"
serial
port
(DB25 or
RJ45)
can
communicate
with
your
computer
or
printer
at
a
baud
rate
of
110
to
115,200
baud
(bits
per
second).
The
second
host/printer
serial
"Aux"
port
can
communicate
at
speeds
from
110
baud
to
38,400
baud.
Any of
these
ports
can
be
used
to
connect
to a
host
computer/modem
or
serial
printer.
Receive
Flow
Control
Because
devices
can
receive
data
faster
than
they
can
process
it,
data
flow
control
(selectable
in
the
PORTS
menu
of
Setup)
should
be
used
to
prevent
data
loss.
Software
flow
control
relies
on
the
Xon
and
Xoff
characters
("g"
and
"e"
characters
in
PC-Term
mode)
to
indicate
when
the
terminal
is
able
or
unable
to
store
further
data.
The
Xon
signal
transmits
the
DCI
character
(1Ih)
and
the
Xoff
signal
transmits
DC3
(13h).
This
terminal
has
a receive
buffer
capable
of
holding
256
bytes
(or
characters).
When
the
buffer
becomes
half
full
(128
bytes),
and
"EIA (or Aux) Rcv"
in
the
Setup
menu
for PORTS is "Xon-Xoff,"
the
terminal
issues
an
Xoff
character,
indicating
to
the
host
that
it
should
stop
transmitting
data.
The
terminal
will
then
continue
to
process
data
until
its
receive
buffer
holds
only
32
bytes.
It
will
then
issue
an
Xon
character
to
the
host,
indicating
that
it
can
resume
sending
data
to
the
terminal.
If
the
"ElA (or Aux) Rev"
is
"No Protocol"
itJ,$~tup,
l:qe
terminal
will
continue
to
accept
characters
into
its
receive
buffer
UIlpl it is full. Additi0I'lal
characters
Will be
lost,
Xon-Xoff
protocol
must
also
be
set
on
the
host
computer
or
printer
for
proper
handshaking.
In
addition
to
software
"receive" flow
control
(Xon-Xoff),
the
serial
host/printer
ports
support
"receive"
hardware
flow
control.
The
EIA
ports
have
an
outgoing
DTR
(Data
Terminal
Ready)
signal.
If
the
DTR
signal
on
the
terminal
is low
and
"EIA Recv" is "DTR"
in
Setup,
then
the
serial
device will
stop
sending
to
the
terminal.
On
the
AUX
port,
the
incoming
DSR
(Data
Set
Ready)
signal
serves
to
signal
the
device
that
the
terminal
is
not
ready
to
receive
more
data,
if "Aux Recv" is "DSR"
in
Setup.
Transmit
Flow
Control
Likewise,
the
terminal
will
understand
the
Xon
and
Xoff
requests
from
the
host
when
it is
transmitting
data
(provided
the
"EIA (or Aux) Xmt" is "Xon-Xoff" in
Setup).
This
is
referred
to
as
"transmit"
flow
control.
This
terminal
will
stop
transmitting
data
to
the
host
or
printer
when
it
receives
an
Xoff (DC3)
code.
If,
however,
the
terminal
needs
to
send
a receive
protocol
character,
it will
transmit
that
character
even
if it
has
received
an
Xoff
code.
When
the
terminal
stops
transmitting,
the
data
will be
buffered
in
the
transmit
buffer
(64
characters
for
the
first
host/printer
port
and
64
characters
for
the
second
host/printer
port).
Once
the
buffer
is full,
additional
keyboard
data
will be
lost.
When
an
Xon
(DCI)
character
is
received,
the
terminal
can
again
send
data
to
the
attached
serial
device.
In
addition
to
software
"transmit"
flow
control
(Xon-Xoff),
the
serial
host/printer
ports
support
"transmit"
hardware
flow
control,
whereby
DSR
on
the
EIA
port
and
DTR on
the
AUX
port
monitor
serial
devices
to
control
the
flow of
data
to
them
(provided EIA
and
AUX
Xmit
is "DSR"
and
"DTR" in
Setup).
For
parallel
printers,
this
terminal
monitors
the
BUSY
and
ERROR
signals
which
are
sent
by
the
printer
to
determine
when
data
transmission
should
be
stopped
or
resumed.
Host/Printer
Port
1
(0825)
This
port,
labeled
"EIA,"
located
to
the
left of
the
video
port,
is
designed
for
connection
to
the
host
(computer
or
modem)
or a
serial
printer
via
a
25-pin
D-shell
(DB25P)
female
connector.
This
port
uses
an
RS-232-C
communication
interface,
is
configured
as
a DTE
(Data
Terminal
Equipment)
device,
and
can
operate
from
110
to
115,200
baud.
The
pins
supported
are
shown
below.