Multi-Tech Systems MT2834MR6 manual Functional Description of the RS-232C Signals

Appendix

Functional Description of the RS-232C Signals

Transmitted Data (TD) — Pin 2 (To modem)

Signals on this circuit are generated by the local computer and passed to the modem’s transmitter. A positive signal is a space (binary 0) and a negative signal is a mark (binary 1). The transmitting computer should hold this line in the marking state when no data is being transmitted, including intervals between characters or words. The TD LED indicates the status of this circuit.

Received Data (RD) — Pin 3 (From modem)

The circuit is the data output of the modem. Data signals received from the remote modem are passed to the local computer on this line. When no carrier signal is being received (pin 8 negative), this line is forced into a marking condition. The RD LED indicates the status of this signal.

Request To Send (RTS) — Pin 4 (To modem)

This signal, from the computer, indicates to the modem that the computer has data to transmit.

Clear To Send (CTS) — Pin 5 (From modem)

This signal indicates to the computer that the modem is ready to transmit any data present on the Transmit Data line (pin 2).

Data Set Ready (DSR) — Pin 6 (From modem)

This signal indicates indicates that the modem is in data mode and is connected to the communications channel. This signal is on during analog-loop-test mode.

Signal Ground (SG) — Pin 7

The SG pin is connected to the modem’s signal ground. It establishes the common ground reference for all the other interface signals.

Carrier Detect (CD) — Pin 8 (From modem)

A high CD signal (positive voltage) indicates that a carrier signal has been received from the other modem. This circuit does not typically turn on in the presence of message circuit noise or out-of-band signals. There is a one-second delay between when the carrier tone is detected and when the CD circuit is turned on.

This signal goes off if received data carrier falls below the receiver threshold for more than 37 ms. When CD is off, the Received Data circuit (pin 3) is held to the marking state.

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