The remotely operated underwater vehicles that the client develops have needs of different kinds of data channels. In order to minimize the need of physical cable between the control unit and a ROV, a multiplex protocol has been developed. The protocol has been designed with the aim of using the bandwidth of the transferring link as efficient as possible.The different kinds of data channels used during this thesis project is; RS232, RS485 and CAN. ROM and FIFO-memories have been used to be able to effectively manage the different data channels. All the reading and sending of these channels have been implemented in FPGA-technology, the coding is made generic so that it will be easier to add more channels to the system in the future.The multiplex protocol is a modified version of the method STDM and it is a proprietary protocol.