IBM 5150 - Page 259

I
QC
Establishing a Link on a Switched Point-To-Point Line
....
1.
Terminal A is in
communications
mode; therefore,
the
'data
~
terminal ready' line
.is
active. Terminal B is in
communication
mode waiting
for
a call
from
terminal
A.
=
~
2.
When
the
terminal A operator
lifts
the
telephone handset,
the
§.
'switch
hook' line
from
the
coupler is activated II.
/') ~
....
3 .
Modem A detects
the
'switch
hook'
line and
activates
the
'off
g.
hook'
line.,
which
causes
the
coupler
to
connect
the
telephone
(I.l
set
to
the
line and
activate
the'
coupler
cut-through'
line
8to
the
modem.
4.
Modem
A activates the 'data
modem
ready' line
lito
the
coupler
(the 'data modem ready' line is on
continuously
in
some modems).
5.
The terminal A operator sets
the
exclusion
key
or
talk/data
switch
to
the
talk position
to
connect
the
handset
to
the
communications
line. The operator then dials
the
terminal B number.
6.
When
the
telephone at terminal B rings, the coupler
activates
the
'ring indicate' line
to
modem B
1m
.
Modem
B indicates
that
the
'ring indicate' line
was
activated
by
activating the 'ring
indicator'
line
lito
terminal
B.
7 . Terminal B activates
the'
data
terminal
ready' line
to
modem
Bill
which
activates
the
autoanswer
circuits
in modem
B.
(The
'data
terminal ready' line
might
already be active in some terminals.)
8. The
autoanswer
circuits in
modem
B
activate
the
'off
hook'
line
to
the coupler
a.
9. The coupler connects modem B
to
the
communications
line
through
the 'data
tip'
and 'data ring' lines
III
and
activates
the
'coupler
cut-
through'
line
lito
the modem. Modem B
then
transmits
an
answer
tone
to
terminal
A.
10.
The terminal A operator hears
the
tone
and sets the
exclusion
key
or
talk/data
switch
to
the
data position (or performs an
equivalent
operation)
to
connect
modem A
to
the
communications
line
through
the
'data
tip'
and 'data ring' lines II.
11. The coupler
at
terminal A deactivates
the
'switch
hook'
line II.
This causes modem A
to
activate
the
'data
set
ready'
lineD
indicating
to
terminal A
that
the
modem
is connected
to
the
communications
line.
The sequence
of
the remaining steps
to
establish
the
data link
is
the same as
the
sequence required on a nons
witched
point·to-
point
line.
When
the
terminals have completed
their
transmission,
they
both
deactivate
the
'data terminal ready' line
to
disconnect
the
modems
from
the line.
)
)
)