1. Field of the Invention
The present invention relates to a multiplex transmission apparatus which has a plurality of communication nodes connected via a multiplex bus, and outputs an operation command signal from a communication node connected to an input switch to another communication node connected to an electrical component via the multiplex bus.
2. Description of the Related Art
Conventionally, as disclosed in Japanese Patent Laid-Open No. 1-143535, a multiplex transmission system has been proposed. In this system, a plurality of communication nodes equipped in, e.g., a vehicle are connected in a network pattern using a common multiplex bus, and the multiplex bus is shared by a plurality of electrical components, thereby simplifying the harness structure for connecting the electrical components and input switches for operating these members.
The multiplex transmission system includes communication nodes which are set in a sleep state, i.e., an inoperative state when an ignition switch is turned off, and communication nodes which are set in a wake-up state, i.e., an operable state by a battery power supply even when the ignition key is not ON. Communication nodes for controlling electrical components such as door lock switches, head lamps, and the like, which must operate when the ignition switch is in an OFF state are maintained in the wake-up state by electrical power supplied from the battery power supply, thereby allowing operations of these electrical components.
When the communication nodes which are to be set in the wake-up state by the battery power supply are always maintained in the wake-up state, a dark current flows to waste battery power. For this reason, when the door locks are locked after the ignition key switch is set in the OFF state, and it is confirmed that none of the electrical components are in operation, the communication nodes are shifted to the sleep state.
More specifically, by detecting the operating states of electrical components or detecting the operating states of input switches, it is confirmed that none of the electrical components are in operation, and thereafter, the communication nodes are shifted to the sleep state. For this reason, if the operating state of at least one of the electrical components cannot be properly detected, the communication nodes cannot be shifted to the sleep state, and waste of battery power cannot be avoided.