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SERIES II INTELLIGENT DATA/FAX MODEMS
Transmit Clock - Pin 15, TC (DB)
Direction: from modem
The TC signal is provided only when the Series II Modem 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 will be 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 pre-
sented by the terminal on the first positive (Off to On) transition of TC
which occurs after the CTS circuit on pin 5 has turned on. The trans-
mitted data is sampled by the modem on negative transition of TC.
Receive Clock - Pin 17, RC (DD)
Direction: from modem
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.
Data Terminal Ready - Pin 20, TR or DTR (CD)
Direction: to modem
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 will force 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