Black Box MD1641A, MD1640A manual Transmit Clock Pin 15, TC DB, Receive Clock Pin 17, RC DD

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

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