Communications interface trace

The communications interface trace monitors the modem interface signals and detects wrong or incompatible use of the modem interface.

To achieve the most accurate sample of the lines, start the trace before varying on the communications lines. This test monitors the following modem interface signals:

Data Terminal Ready (DTR): Data terminal equipment (DTE) uses this signal to show the modem that the DTE is ready to transmit and receive data.

Data Set Ready (DSR): For nonswitched telephone lines, the active DSR signal shows that the modem is powered-on and ready to transmit and receive data. For switched telephone lines, the active DSR signal shows that the modem is connected to the telephone line and is ready to transmit data.

Request To Send (RTS): The request to send trace uses this signal to activate or deactivate the modem's modulator lines. If the DSR signal is active, the RTS signal causes the modem to activate the carrier signal.

Ready For Sending (CTS): The modem activates this signal in response to the Request To Send signal when the modem is ready to transmit data. When the CTS signal is active, the DTE can send data on the transmitted data line.; CTS delay is the time between the RTS signal active condition and the CTS signal active condition. On most nonswitched telephone line modems, there are three CTS delay options, ranging from 0 to 250 milliseconds (ms). Switched telephone line modems, operating in half-duplex mode, are normally set for 150 to 250 ms of CTS delay.

Carrier Detect (CD): The modem uses this signal to show the DTE that the modem is receiving an acceptable carrier signal. Because of hardware limits on taking short frame samples, the carrier detect signal might not be accurate. In this condition, an asterisk (*) takes the place of the sample data. The status is still correct.; This test displays five of the modem interface signals in a graphic format, showing the time relationship of the signals to each other.