A system for data transmission between two devices, including an output device having a binary output interface and a first field device having a binary input interface connected in a signal-transmitting manner to the binary output interface via a unidirectional connection. The output device includes a signal processing module which is set up to convert a data set to be transmitted to a binary, discrete-time signal in accordance with a serial protocol. The first field device includes a signal processing module which is set up to convert the received binary, discrete-time signal to the data set in accordance with the serial protocol. The invention further relates to a valve system.