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Ekctrical Characteristics
Call Orgination Status (COS/204). The ACU generates signals on this circuit to
indicate the status of the automatic call origination procedures. The ON condi-
tion, during an automatic call procedure, indicates that ( 1) the ACU has complet-
ed its calling function and (2) control of the communication channel has been
transferred to the modem interface.
Note: If Data Terminal Ready is not ON when COS comes ON, the call
should be disconnected immediately.
Digit Leads (NBl/206, NB2/207, NB4/208, NB8/209). The IBM 3704 and
3705 generate signals on these circuits to present the dialing digit in binary form
to the ACU. (The low-order position is NBl.)
Data Line Occupied (DL0/203). The ACU generates signals on this circuit to
indicate the condition of the communication channel. The ON condition indicates
that the communication channel is in use for calling, data communication, voice
communication, or testing. The OFF condition indicates that that the ACU may
originate a call if PWI is active.
The IBM 3704 and 3705 interfaces to external automatic calling units complies
with the electrical requirements of EIA RS-366 as highlighted in the following
paragraphs.
All voltages are measured at the connector with respect to Signal Gound (AB).
The output line delivers between
5
volts and 15 volts into a resistance of at least
3,000 ohms but not more than 7 ,000 ohms. The input circuit responds to voltage
between 3 volts and 25 volts. The polarity of the signals depends on the follow-
ing:
Data
Polarity
(Dial Digits)
Logic Control
+
Space
0
ON
Mark
1
OFF
The terminating impedance of the receiving end of the interchange circuit must be
at least 3,000 ohms but not more than 7 ,000 ohms. The capacitance measured at
the interface connector should not exceed 2,500 pF. The open-circuit voltage of
the imput circuits should not exceed 2 volts of either polarity. A short circuit
between any two conductors (including ground) must not result in a current in
excess of one-half ampere.
For the data and timing circuits, the rise and fall time through the +3 volt to -3
volt range should not exceed either one millisecond or three percent of the nomi-
nal bit time, whichever is less. Conversely, the maximum instantaneous rate of
change (skew rate) through the transition region, +3 volts to -3 volts, must not
exceed 30 volts/microsecond.
The following control lines, when used, are considered 'failsafe' lines:
Call Request (CRQ/202)
Power Indication (PWl/213)
The power-off source impedance of the sending end of the 'failsafe' lines should
be at least 300 ohms, measured at an applied voltage of not greater than ± 2 volts.
Communication Interfaces 13
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