Abstract: An interface is connected between an OCIA type port and a mailing system peripheral, such as a weighing cell. The interface comprises an input data circuit, operatively connected to a serial data input line and to an associated input clock line, for receiving serial data input words comprising 8 serial data bits and an end-of-message (EOM) bit. The input circuit converts the serial input words into parallel form and transfers them to a programmable interface controller. The interface also includes an output circuit for transforming parallel output words from the interface controller into serial format. The output circuit is operatively connected to a serial data output line and an output data clock line from the OCIA type port. When an output data word is loaded into the output circuit the output line is forced to a predetermined logical level signalling the port the data is available. The port then provides a series of clock pulses to shift the data word out from the output circuit.