DATA TRANSMISSION SYSTEM WITH TEST LOOP FACILITIES

摘要

When testing a data transmission system comprising two transmission devices it is feasible that the test loops of both transmission devices are closed so that a latched (locked-in) state is created, wherein the loop signal continuously circulates from one transmission device to the other thus preventing a return to the normal state of data transmission via the two lines. It is the object of the present invention to test the data transmission system without incurring a latched state. According to the present invention at least one bit of the loop signal - adapted to be transmitted to the first transmission device via the second transmission device - is changed before it is re-transmitted to the second transmission device. Use in data transmission systems adapted to operate in outgoing and incoming direction, in particular in the transmission of envelopes.