VHDL Modelling of Glue Logic of 1553b Interface Board
In the satellite launch vehicle, the Avionics system is proposed to be based on MIL-STD 1553B BUS. A number of interface modules for application such as sensor data acquisition, vehicle sequencing, control generation, command posting etc. are being designed with this interface. These interface modules are then connected to the onboard computers via the 1553B BUS.
These modules have to be tested separately and evaluated and also confirm their compliance with the 1553B BUS standard before being integrated as the Avionics System. The PC/AT based MIL-STD 1553B interface board can be used as a standard test system for the module level test. The newly developed interface board can be integrated in the PC bus which guaranteed for 0 microsecond interword gap.
Tri-state buffers are used to isolate the CPUs data and address lines. Since the data transfer with the board is 16 bits, only even addresses of the CPU are required. The address bus from SA1 to SA9 is considered and utilized. The interface hardware is designed as a 16 bit AT interface card to an IBM PC/AT compatible computer.
The VHDL advantage
Traditional design techniques such as Karnaugh maps are typically used to generate design equations that are implemented in a PLD. Using a simple language with syntax for entering combinational and registered equations, the designer enters the design equations in a data file. The equations are then synthesized by software, which produces a data file to use in programming the PLD.
For larger systems that use CPLDs, FPGAs, or ASICs the traditional design methodology described above is not feasible. Generating equations with traditional techniques is time consuming and prone to mistakes. Tracking errors in equations can also be difficult. Schematic capture offers several advantages. For example, it provides a graphical view of the design, and with software tools that support schematic hierarchy, it provides for design modularity. But as means for capturing large designs, even pure schematic capture has its drawbacks:
1).Control logic must still be generated using traditional design techniques;
2).Schematics can be difficult to maintain because the intent of the design is often clouded by its implementation.
3).A schematic must often be accompanied by documentation to describe design's functionality.
MIL-STD-1553B defines the term Time Division Multiplexing (TDM) as "the transmission of information from several signal sources through one communications system with different signal samples staggered in time to form a composite pulse train." For our example in Figure 1b, this means that data can be transferred between multiple avionics units over a single transmission media, with the communications between the different avionics boxes taking place at different moments in time, hence time division.
Since its inception, MIL-STD-1553 has found numerous applications. Notice 2 to the standard has even removed all references to "aircraft" or "airborne" so as not to limit its use. While all the programs to which the standard has been applied are too numerous to be covered here, the following is a summary of its uses. While the standard has been applied to satellites as well as payloads within the space shuttle (it is even being used on the International Space Station), its military applications are the most numerous and far ranging.
It has been employed on large transports, aerial refuelers , and bombers, tactical fighters, and helicopters. It is even contained within missiles and serves, in some instances, as the primary interface between the aircraft and a missile. The Navy has applied the data bus to both surface and subsurface ships. The Army, in addition to its helicopters, has put 1553 into tanks and howitzers.
Commercial applications have applied the standard to systems including subways, for example the Bay Area Rapid Transit (BART), and manufacturing production lines. MIL-STD-1553B has also been accepted and implemented by NATO and many foreign governments. The UK has issued Def Stan 00-18 (Part 2) and NATO has published STANAG 3838 AVS, both of which are versions of MIL-STD-1553B.
The broad acceptance and application of MIL-STD-1553B has also fostered the development of other standardization efforts. MIL-STD-1773 is a fiber optic version of 1553B. And MIL-STD-1760A, the Aircraft/Store Interconnect, has 1553B embedded within it.