New Data Bus Interface Technique

Data bus systems as defined in MIL-STD-1553B are widely used in aerospace instrumentation systems for digital data transmissions between units on the bus. Although the bus is protected against a short circuit which may occur in the remote unit electronics or transformer, it has no protection against a cable termination failure. Open or short failure along main bus cable results in failure of the entire bus system. A new data bus interface technique is described which is insensitive to cable termination failure. The central feature of this new interface circuit is that communication between main unit and remote units is not affected by the cable termination failure. In applications such as multistage missiles, no provisions need be made for retermination in the cable characteristic impedance after stage separation. The key to this new technique is a directional coupling transformer which is only slightly more complicated than standard interface transformers. Design equations for directional coupling transformer and experimental results of new data bus systems are presented.