Communication system, communication apparatus, and communication control method

A communication apparatus as a slave that can communicate with a master, comprising:

• a communication section, when the master transmits a start request signal to said communication apparatus, for receiving the start request signal,
• wherein said communication apparatus can take any of a start state in which said communication apparatus can communicate with the master, a communication control state in which at least said communication apparatus can receive the start request signal transmitted by the master and makes a transition to the start state upon reception of the start request signal, or a standby state in which power is less consumed than in the start state or the communication control state,
• wherein said communication apparatus further comprises a state control section for repeatedly operating so that, independently of any signal from the master, said communication apparatus in the standby state is switched to the communication control state at a predetermined timing and is switched to the standby state when the communication control state continues for a predetermined time period without receiving the start request signal, and wherein said slave further comprises a sensor communicating section which produces a communication state request so that the slave in the standby state is switched to the communication control state.