Abstract: An interface for a data processing system wherein data processing units communicate via a multiple line data channel and a control channel. The interface transmitter converts control signals from the data processor into mulitple bit protocol words, whereas data signals are split into multiple byte portions. The protocol words and data byte portions are then transmitted serially over a single line, such as a fiber optic cable or an RF link. The interface receiver section serial-to-parallel converts the incoming bit stream to restore the protocol and data signals. Appropriate control signals are issued to the associated data processing unit in response to received protocol signals, and data signals are parallel loaded to the unit. The use of an interface at each data processing unit accommodates full duplex operation between the units via a minimum number of connecting links, e.g., two links for fiber optic systems, one link for an RF system.