Signal supplying unit having means for selecting signal in accordance with terminal connection

A signal supplying unit comprising:

• a first terminal;
• a second terminal;
• a first signal source, coupled to said first terminal, for outputting a first signal;
• a second signal source, coupled to said second terminal, for outputting a second signal;
• a third signal source, coupled to said second terminal, for outputting a third signal;
• detecting means, coupled to said first terminal, for detecting whether or not said first terminal is coupled to a terminal of an external unit and for outputting a detecting signal;
• wherein said detecting means has a first resistor connected between a power supply and said first terminal, a second resistor connected between the terminal of said external unit and the ground and voltage detecting means for detecting whether or not a voltage at said first terminal is greater than a predetermined reference voltage;
• and
• selecting means, coupled to said detecting means, for selectively supplying either said second signal output from said second signal source or said third signal output from said third signal source to said second terminal in accordance with said detecting signal output from said detecting means.

A signal supplying unit comprising:

• a first terminal;
• a plurality of terminals;
• a first signal source, coupled to said first terminal, for outputting a first signal;
• a second signal source for outputting a second signal;
• a third signal source for outputting a third signal, said second and third sources being coupled to one of said plurality of terminals;
• detecting means, coupled to said first terminal, for detecting whether or not said first terminal is coupled to a terminal of an external unit and for outputting a detecting signal;
• and
• selecting means, coupled to said detecting means, for selectively supplying either said second signal output from said second signal source or said third signal output from said third signal source to said one of said plurality of terminals in accordance with said detecting signal output from said detecting means.

A signal supplying unit comprising:

• a first terminal;
• a plurality of terminals;
• a first signal source, coupled to said first terminal, for outputting a first signal;
• a second signal source for outputting a second signal;
• a third signal source for outputting a third signal, said second and third signal sources being coupled to one of said plurality of terminals;
• detecting means, coupled to said first terminal, for detecting whether or not said first terminal is coupled to a terminal of an external unit and for outputting a detecting signal;
• wherein said detecting means has a first resistor connected between power supply and said first terminal, a second resistor connected between the terminal of said external unit and the ground, and voltage detecting means for detecting whether or not a voltage at said first terminal is greater than a predetermined reference voltage;
• and
• selecting means, coupled to said detecting means, for selectively supplying either said second signal output from said second signal source or said third signal output from said third signal source to said one of said plurality of terminals in accordance with said detecting signal output from said detecting means.

A signal supplying unit comprising:

• a plurality of terminals;
• a plurality of signal sources, each of said plurality of signal sources outputting a signal;
• detecting means, coupled to at least one of said plurality of terminals, for detecting whether or not at least said one of said plurality of terminals is coupled to a terminal of an external unit;
• and
• selecting means, coupled to said detecting means, for selecting signals to be supplied to said plurality of terminals from signals output from said plurality of signal sources in accordance with a detecting result obtained by said detecting means.

A signal supplying unit comprising:

• a first terminal;
• a second terminal;
• a third terminal;
• signal sources for respectively outputting a first, second, third, fourth, fifth and sixth signals;
• detecting means;
• coupled to said second and third terminals, for detecting whether or not each of said second and third terminals is coupled to a terminal of an external unit;
• and
• selecting means, coupled to said detecting means, for selecting signals to be supplied to said first, second and third terminals from the first, second, third, fourth and fifth signals output from said signal sources in accordance with a detecting result obtained by said detecting means.