A method for synchronizing bus subscribers of a distributed control automation system communicating with one another via a serial data bus, wherein the method is characterized in that one of said bus subscribers having at least one communication controller, wherein one communication controller of said communication controller named following communication controller cooperates via three freely programmable communication-ALUs (RPA, TPA, PEA), namely named the first communication-ALU, the second communication-ALU and the third communication-ALU, with a downstream control device and that the method comprising the following steps: • said communication controller detects the occurrence of a specific date or event, • said communication-ALUs (RPA, TPA, PEA) autonomously and without said downstream control device performs completely deterministic the synchronous control functions, whereby le method comprising the following steps: - said first communication-ALU decodes corresponding to the transmission rate of the received bit or nibble serial data stream and converts it into a parallel representation, - said second communication-ALU encodes data from a parallel representation into a bit- or nibble-serial data stream and applies it with the correct transmission rate to the line and - said third communication-ALU controls the transmission and reception history of a related data packet and • between the synchronization times the measurement and control values are exchanged between said communication controller and said control device, whereby said communication controller, said three communication-ALUs (RPA, TPA, PEA) and said control device are adapted such, that the interrupt latency period of the downstream control device do not affect the synchronization. • said communication controller detects the occurrence of a specific date or event, • said communication-ALUs (RPA, TPA, PEA) autonomously and without said downstream control device performs completely deterministic the synchronous control functions, whereby le method comprising the following steps: - said first communication-ALU decodes corresponding to the transmission rate of the received bit or nibble serial data stream and converts it into a parallel representation, - said second communication-ALU encodes data from a parallel representation into a bit- or nibble-serial data stream and applies it with the correct transmission rate to the line and - said third communication-ALU controls the transmission and reception history of a related data packet and - said first communication-ALU decodes corresponding to the transmission rate of the received bit or nibble serial data stream and converts it into a parallel representation, - said second communication-ALU encodes data from a parallel representation into a bit- or nibble-serial data stream and applies it with the correct transmission rate to the line and - said third communication-ALU controls the transmission and reception history of a related data packet and • between the synchronization times the measurement and control values are exchanged between said communication controller and said control device, whereby said communication controller, said three communication-ALUs (RPA, TPA, PEA) and said control device are adapted such, that the interrupt latency period of the downstream control device do not affect the synchronization.