QSG-15850
6
Holt Integrated Circuits
current-limiting resistors in series with the bus connection. When configuration jumpers are set for
direct-coupled operation, current-limiting resistors are provided on the break-out board.
Transformer-coupled 1553 bus interface is the predominant configuration used for terminal connection.
This diagram shows a network comprised of three transformer-coupled terminals: a Bus Controller (BC)
and two Remote Terminals (RTs). Stub cables must be < 20 feet (6.1 meters).
The HI-15850 Signal Break-Out Board (and user-provided protocol logic) takes the place of the BC or one
of the RTs in the above diagram.
As seen above, each terminal’s stub cable connects to the 1553 bus through a “bus coupler,” which is
typically an off-the-shelf hardware component comprised of coupling transformer(s) for one or more
terminal stubs (each with its own pair of internal current-limiting resistors). Two bus couplers are shown
above. The bus couplers have a bus connection jack at each end for serial connection into the 1553 bus
structure. Each end of the bus has a 78Ω terminator. Holt application note AN-550 provides additional
information about the direct- and transformer-coupled configurations.
Dummy Resistor Bus Load Option
The HI-15850 Signal Break-Out Board provides 12 solder jumper or shunt locations for selection of
direct- or transformer-coupled operation. The jumpers also select on-board resistor dummy bus load or
off-board conventional 1553 bus connection, shown above. When enabled, the on-board dummy load
replaces the stub cable assembly in the diagram and everything above it; the resistor load appears
