Abstract: A communication system of the multiplex type between a master processing unit incorporating a microprocessor and slave units associated in particular with electrical devices in a vehicle for activating or controlling at least one electrically functioning component of the corresponding device the slave units being connected in groups to the master unit by means of corresponding communication channels, and in which these slave units include logic means for the exchange of communication messages with the master unit and are capable of independently initiating transmission towards the master unit; such messages in particular include a first field for identification of the slave unit which is sending or is to receive the communication, a second data field, and a preliminary field used to activate such units from a resting state of minimum power consumption.