Abstract: A communication network, such as an audiovisual system, on an automobile has a master unit and a plurality of slave units which are connected to a common communication bus. The display unit displays operation of the other slave units based on display data transmitted from the other slave units. The display data includes character data regarding a character to be displayed and/or standard bit data common with the slave units. The character data and/or the standard bit data may be positioned at the leading end of the display data.

Abstract: A communication network, such as an audiovisual system, on an automobile has a master unit and a plurality of slave units which are connected to a common communication bus. When the communication network starts operating, connection confirmation request information is transmitted from the slave units to the master unit. The master unit awaits connection confirmation request information from at least one of the slave units for a predetermined period of time after the communication network starts operating. Thereafter, the predetermined period of time is extended if the reception of connection confirmation request information from all the slave units that were connected when the connection network stopped operating in a preceding cycle is not completed. If reception acknowledgement information from the master unit is not detected for a predetermined period of time, then the slave units automatically enter a low power consumption mode.

Abstract: A communication network, such as an audiovisual system, on an automobile has a master unit and a plurality of slave units which are connected to a common communication bus. Each of the master and slave units is capable of successively issuing a plurality of command data through asynchronous transmission to another unit and returning acknowledgement data in response to the command data transmitted from another unit. The units add received command data to acknowledgement data when the acknowledgement data is to be returned. The command data includes first command data requiring acknowledgement data and second command data requiring no acknowledgement data. Each unit handles the first and second command data differently when the acknowledgement data is to be returned. When communication data is to be transmitted between the units, major classification data and subclassification data, depending on the contents of the communication data, are added to a leading portion of the communication data.