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JUMP AND RETURN JUMP INSTRUCTIONS
PERIPHERAL AVIONICS SYSTEMS

Aviation Electronics Technician 1 (Organizational)
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Execution of a return jump instruction causes the address of the next instruction to be executed in the main program to be stored (usually in the entry cell of the subroutine). It then causes the instruction of the second cell of the subroutine to be executed. The last instruction to be executed will usually be a straight jump to the address contained in the entry cell. Since a jump instruction specifies the address of the next instruction to be executed, the computer is provided with a means of returning to the main program once the subroutine has been executed. PROGRAM CONSTRUCTION The process of writing a program is broken down into six basic steps. 1. Statement. A statement forms a clear compre- hensive statement of the problem. 2. Analysis. Analysis consists of laying out the problem in a form that will lend itself to arithmetical and/or logical analysis, determining what logical decision must be made, and if data manipulation is required. 3. Flow diagram. A flow diagram, or chart, is an expansion of the steps in which special symbols are used to represent the various operations to be performed and the sequence in which they are to fall. 4. Encoding. The process of converting the operations listed in the flow chart into language the computer will use, either machine instructions, words, or compiler statements. 5. Debugging. The process of locating errors in the program is called “debugging.” Various techniques are available for this purpose. A program may be written to include some aids for itself, or a separate debugging program may be run to test the operation of a malfunctioning program. For a simple program, a trial solution may be done on paper, and the computed results compared with those actually obtained at each step. 6. Documentation. Documentation is very important because later changes may be warranted in a program, or it may be desirable to use subroutines from another program. Proper documentation will ensure that this can be accomplished. Documentation should include the following: l Program title . Problem statement l l l l l l l l Programmer’s name Date Memory area used and/or number of cells used Registers used I/O devices required Flow diagram(s) Hard copy (program listings, especially a listing of the coded instructions) Program tapes FLOW CHARTING The programmer constructs a program “map” in determining a solution to a problem. This map is commonly called a flow chart and serves a multitude of important functions. The flow chart maps the logical steps required, decisions to be reached, and paths to be followed as a result of the decisions. When properly annotated, it defines input/output requirements, address allocations, data accuracy considerations, and register usage. A flow chart is valuable when debugging a program and when making future changes. Flow charting can be constructed at various levels of complexity. A high-level flow chart consists of a few symbols and presents a broad overview of the problem. A low-level flow chart may approach a one-to-one correspondence between flow chart symbol and program instruction. Usually, there will be several flow charts for a program area. These may be compared to the prints found in a maintenance manual. These prints include a block diagram to show the relationship of major units (high-level), functional block diagrams showing the major circuits in a unit (intermediate-level), and the schematics of the circuits (low-level). Flow charts should beat such a level that they will implement all the uses previously discussed. MAINTENANCE PROGRAMS As we have previously stated, a routine or program is a series of instructions that control the operations of a computer. Each instruction is used to cause some action that is part of the overall task the computer must perform. Therefore, an instruction may be considered as the basic building block of a computer program. 8-15







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