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a) The local modem is connected to a communication channel ('OFF
HOOK" in switched service).
AND
b) The local modem is not in test (local or remote), talk (alternate
voice), or dial mode.
AND
c) The local modem has completed, where applicable:
1. Any timing functions required by the switching system to com-
plete call establishment, and
2. The transmission of any discrete answer tone, the duration of
which is controlled solely by the local modem.
If
the local modem does not transmit an answer tone, or if the
duration of the answer tone is controlled by some action of the
remote modem, the ON condition must be presented as soon as
all the other above conditions (a, b, and c-1) are satisfied.
Signal Ground (AB/102). This conductor establishes the common ground refer-
ence for all interface lines.
Received Line Signal Detector (CF /109). The modem generates signals on this
circuit. The ON condition on this circuit is present when the modem is receiving a
signal that meets its suitability criteria. These criteria are established by the
modem manufacturer.
New Sync (Pin 14). To allow for faster receiver bit synchronization for subse-
quent messages, the IBM 3704 and 3705 may provide signals on this circuit that
may be used by the modem to squelch the receiver signal element timing clock.
Transmitter Signal Element Timing (DB/114). Signals on this circuit, when
generated by synchronous modems, are used to provide the IBM 3704 and 3705
with 'signal element timing' information. The IBM 3704 and 3705 change the
transmitted data signals simultaneously with
OFF to ON
transitions of this
circuit. The modem must sample bits with the
ON to OFF
transitions on circuit
DB/114. The
ON to OFF
transitions should occur in the center of each signal
element. The Transmitter Signal Element Timing pulses must have an accuracy of
0.01 %. This timing signal must be a square wave form with a duty cycle of 50%
±
10%. Transmitter Signal Element Timing pulses, when provided by a modem,
must be continuous whenever circuit CC/107 (Data Set Ready) is ON.
Receiver Signal Element Timing (DD/115). Signals on this circuit, when generat-
ed by synchronous modems, are used to provide the IBM 3704 and 3705 with
'received signal element timing' information. The transition from ON to OFF
must indicate the center of each signal element on circuit BB/104 (Received
Data). This signal, when provided to the IBM 3704 and 3705, must be continuous
during a receive operation.
Modem Wrap (Local Test
Pin
18). The IBM 3704 and 3705 may provide signals
on this circuit. An active level indicates that diagnostic mode has been set in the
IBM 3704 and 3705 line interface and that the modem should go into local test.
Connect Data Set to Line (CD/108.1). The IBM 3704 and 3705 generate signals
on this circuit to control the switching of the modem to the communication
channel. The ON condition must cause the modem to connect to the communica-
tion channel and to maintain this connection.
Communication Interfaces 7
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