SECTION 574-123-lOOTC
Operation of the test (TST) pushbutton (locking)
causes received signals to be retransmitted to the
test center for maintenance purposes. A lamp,
associated with each pushbutton, illuminates the
pushbutton whenever that pushbutton has been
operated and the operating condition exists. The
ANS lamp is pulsed in response to ringing signals
of an incoming call, and lights continuously when
the call is answered. The CLR lamp is automat-
ically extinguished 1.5 seconds after the push-
button has been depressed, and disconnect is
completed.
2.05 A steady mark signal blinds the associ-
ated teletypewriter during all intervals,
except when in the connect condition. This
prevents spurious characters from being printed
except when due to loss of signals, circuit noise,
or deliberate break or space-disconnect signals.
Progress of a Call
2.06 To originate a call, the ORIG push-
button (Figure 2) is momentarily
depressed. This connects the station to the line
and lights the ORIG lamp. During the period of
time in which connection is being made, the
telephone central office makes no time measure-
ments. When the ORIG pushbutton is closed, the
call control unit is connected to the telephone
line through the data set and an off-hook condi-
tion is set up. The amplifier is connected into the
circuit so that the dial tone from the central
office is heard. The called station is dialed while
the amplifier monitors the progress.
2.07 At the called station audible and visible
signaling devices are operated. The
called station goes off hook and into the connect
condition upon operation of the ANS pushbutton
circuit, by manual or automatic means, at the
distant point. At this time, there is a nonsignaling
interval of 1.225 seconds during which
accounting and toll recording facilities at the
telephone exchange will be cleared. Following the
nonsignaling interval, the called station transmits
its F2 mark tone and sets its monitoring timer to
respond to the Fl mark tone from the calling
station. When the continuous F2 mark tone is
received at the calling station for a period of 1
second, indicating that a station has answered, it
will go into the connect condition and turn on its
motor. When the continuous Fl mark tone is
received at the called station for an interval of 1
second, it will go into the connect condition. The
station may now acknowledge the call either by
operator keyboarding, or by automatic answer-
back message transmission. The monitoring timers
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at both stations are set to respond to reception of
a space tone from the distant station. Traffic can
now be exchanged from either station on a
half-duplex basis.
Disconnecting a Call
2.08 During the time the two stations are
connected (traffic interval), either
station can initiate a disconnect as follows:
(a) A call is normally terminated by the
end-of-transmission (EOT) code
combination which provides fast disconnect
without introducing hit characters. This is
accomplished by the data set in response to
EOT contact closures in function boxes of
both the sending and receiving teletype-
writers.
(b) A call connection can also be cleared
manually by momentarily depressing
the CLR pushbutton (Figure 2). Operation
of the CLR pushbutton at either station will
cause transmission of a spacing signal of
1.5-seconds duration, after which the station
originating the disconnect will discontinue
its tone transmission and go back on hook.
The other station, after receiving the spacing
signal for 1 second, will automatically trans-
mit its 1.5-second spacing signal and then go
on hook. Both stations will then be back in
their original idle condition in which calls
can be either originated or accepted.
Answering a Call
2.09 To answer a call manually, momen-
tarily depress the ANS pushbutton
(Figure 2). This connects the station to the line
and lights the ANS lamp. The lamp remains
lighted until the answer mode is terminated.
Manual answering is necessary only when the
automatic answer-back circuit is disabled. The
automatic answer-back circuit is disabled by
low-paper contacts, data set relay contacts (when
in local mode), and the OUT OF SERV. key.
2.10 Call control units equipped with auto-
matic answering facilities will respond
to received ringing signals, turning the teletype-
writer on at the end of the ringing interval and
proceeding through to the connept condition.
Automatic message answer-back is a part of this
feature. The presence of an operator is required in
order to complete disconnect and return the
teletypewriter to idle condition. For unattended
service, an automatic disconnect timing device
