Multitech MT2834MR Owner's Manual page 96

PN 88300150
The TC signal is provided only when the MT2834MR is used 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 which occurs after the CTS circuit on pin 5 is turned on. The
transmitted data is sampled by the modem on negative transition of TC.
The RC signal has the same characteristic of Transmit Clock, with the exception that it is used to provide
the computer or terminal with timing information for its Receive Data (pin 3) circuit. The negative transition
(On to Off) of RC indicates the center of each signal element on the Received Data circuit.
This signal (TR or DTR) provides a means for the terminal or 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 mSec forces the modem to disconnect.
The most common use of DTR is in automatic answer applications. A high DTR signal is required by the
modem to answer a call. 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-auto
answer applications it is advisable to leave DTR on using the modem's DIP-Switch option. This is the
standard factory setting. An alternative is to provide a constant high DTR from the terminal or computer.
The Data Terminal Ready (DTR) LED indicates the status of this signal.
This signal remains on for the duration of the ringing signal. When a ring signal is received by the modem,
the modem automatically answers after the first ring. The modem can answer after a specified number of
rings which can be programmed in AT Command Mode, but if none is specified, the modem answers after
the first ring.
Supplies the same function as transmit clock on Pin 15.
The Terminal Busy (OOS) circuit is not defined in the RS232C standard, but is used by us and most
manufacturers to make the phone lines busy to incoming phone calls. Pin 25 is not typically connected to
the RS232C interface when shipped from the factory; it can be ordered connected as an option. If pin 25
is connected and is brought high, the modem is placed Off Hook, and is busy to incoming calls.
4/3/01
Transmit Clock - Pin 15, TC (DB)
Direction: from modem
Receive Clock - Pin 17, RC (DD)
Direction: from modem
Data Terminal Ready - Pin 20, TR or DTR (CD)
Direction: to modem
Ring Indicator - Pin 22, RI (CE)
Direction: from modem
External Transmit Clock - Pin 24, XTC
Direction: to modem
Terminal Busy (Out of Service) - Pin 25, OOS
Direction: to modem
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