Patent ID: 7668993

Claim:
A device control method in a system comprising a) a plurality of units connected to a bus, each unit including at least one of an input plug connected to the bus for inputting an input signal to the unit from the bus and an output plug connected to the bus for outputting an output signal to the bus from the unit, and b) a subunit included in the unit, the subunit connected to the bus through the unit and having at least one of a destination plug connected to the input plug for inputting a destination signal to the subunit from the bus and a source plug connected to the output plug for outputting a source signal to the bus, said method comprising the steps of: a) signaling a command to a first unit connected to the bus for inquiring a status of the input plug or signaling the command to the subunit included in the first unit for inquiring a status of the source plug; and b) receiving a single of a response to the command provided by the first unit signaled in step a) or the subunit signaled in step a), wherein the response includes information indicating that a virtual signal output is virtually input into the first unit while the first unit actually receives a signal from the bus, and the information further indicates that the virtual signal output is virtually received from a second unit connected to the bus.