| 摘要 |
An automatic detection and selection circuit resident in a DCE is provided. The circuit is coupled to the DCE interface connector and detects receipt by the DCE of V.35 and RS-232 transmit data signals, distinguishes between those signals, and selects circuitry for passing the data therethrough. The circuit comprises a switch coupled to a first TX data terminal (pin 2 or P) of the DCE interface connector, first and second line receiving circuits, a microprocessor, and a relay. The first line receiving circuit is coupled to a first pole of the switch and to the second TX data terminal (pin S) of the DCE interface connector and provides indications as to whether or not an input signal is present at at least one of pins P and S. The second line receiving circuit is coupled to the second pole of the switch and provides indications as to whether or not a valid RS-232 transmit data signal is detected. The microprocessor is coupled to the outputs of the line receiving circuits, and based on the indications output thereby, appropriately controls the relay, and hence the switch. The microprocessor first checks in a V.35 mode as to whether a data signal is being received. It then checks in a RS-232 mode as to whether the data signal is a valid RS-232 signal. If not, it switches the circuit back to the V.35 mode. |
