A data transmission control processing system is described which can easily realise the reading from and writing to the memories of other terminals in a network. The proposed system provides for writing to the memory of the other terminal in a way which is similar to the memory reading sequence of the D2B system, and thus simplifies the realisation of the reading/writing control sequence while reducing the number of control messages which are necessary. The system can easily cope with possible future expansions in the number and type or read/write control signals.