It looks like this might be an avionics 1553 processor or interface/controller for unibus PDP/VAX. ( from the STC 1553 transcievers ) It looks too complex to be only a 1553 serial bus interface, but with the 2901 bit slice and 2910 microsequencer, it might be a complete CPU to do development on a unibus host. MIL-STD -1553 is a bidirectional, 1 Mbit serial, TDM, manchester II biphase encoded, dual-redundant avionics bus that runs on stub terminated twisted shielded pair media. (hence the BNCs). It supports 31 TDM "terminals" in a 20 bit paritied words (3sync+16data+P). Messages contain at least one command word and max 32 16 bit data words, on 5 bit addresses/subadresses. MIL-STD-1773 defines the newer optical cabling fiber based bus. 1553 was typically used in military and fighter aircraft for interconnecting INS/GPS, fly by wire, engine management, and even flight controls. The standard dual redundant paths improve reliability - thus cuts down on airplane crashes somewhat ;) The DC/DC might be for generating an isolated or odd supply for the STC transceivers, even though they are generally transformer coupled and resistor terminated in the wiring hardness. Some google links show that the navy used an IMUTS Unibus based system to test carrier aircraft IMU/INS : http://www.globalsecurity.org/military/library/policy/navy/ntsp/imuts-a.htm An online resume indicated development of a VMS driver for a VAX based 1553. see http://www.testsystems.com/pdf/overview.pdf http://www.ampol-tech.com/what1553.htm regards Heinz