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Test Voltage (+V) — Pin 9
This test pin has 330 ohms of resistance to +12 volts DC. It can be used to strap other
signals high. For example, if the terminal does not supply a DTR (Data Terminal Ready)
signal, pin 9 can be jumpered to pin 20 (DTR) on the RS-232C connector or cable to force
DTR on.
High Speed (HS) — Pin 12
The high state of this circuit indicates that the modem is in the high speed (1200 bps) mode.
This circuit is commonly used to signal the computer or terminal to which the modem is
connected to switch to its 1200 bps setting.
Transmit Clock (TC) — Pin 15
The TC signal does not apply to the MT2834MR6, since it is used only in the synchronous
mode. The clock is a square wave and is used to provide the computer or terminal with
timing information for its Transmit Data circuit (pin 2). This clock is provided on the interface
at all times when the modem is in synchronous mode.
The first signal element of the Transmitted Data signal should be presented by the terminal
on the first positive (off to on) transition of TC after the CTS circuit on pin 5 is turned on. The
transmitted data is sampled by the modem on negative transitions of TC.
Receive Clock (RC) — Pin 17
The RC signal has the same characteristics as the TC signal, with the exception that it is
used to provide the computer or terminal with timing information for its Receive Data (pin 3)
circuit. The RC signal's negative transition (on to off) indicates the center of each signal
element on the Received Data circuit.
Data Terminal Ready (DTR) — Pin 20
The DTR signal provides a means for the computer to control the modem's connection to
the communications channel. A high DTR signal is required by the modem to be able to
communicate. Turning DTR off for more than 50 ms forces the modem to disconnect.
The most common use of DTR is in autoanswer applications. A frequently used method is to
have the computer turn on DTR in response to RI (Ring Indicator), which allows the modem
to answer. Later, DTR is turned off at the conclusion of the log off procedure, which forces
the modem to disconnect, enabling it to receive another call. In non-autoanswer
applications it is advisable to leave DTR on. This is the standard factory setting. An
alternative is to provide a constant high DTR from the terminal or computer.
(From modem)
(From modem)
(From modem)
(From modem)
(To modem)
Appendix
108
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