Aviation Electronics Technician 1 - Historic Naval Ships Association

Execution of a return jump instruction causes theaddress of the next instruction to be executed in themain program to be stored (usually in the entry cell ofthe subroutine). It then causes the instruction of thesecond cell of the subroutine to be executed. The lastinstruction to be executed will usually be a straightjump to the address contained in the entry cell. Sincea jump instruction specifies the address of the nextinstruction to be executed, the computer is providedwith a means of returning to the main program oncethe subroutine has been executed.PROGRAM CONSTRUCTIONllllllllProgrammer’s nameDateMemory area used and/or number of cells usedRegisters usedI/O devices requiredFlow diagram(s)Hard copy (program listings, especially alisting of the coded instructions)Program tapesThe process of writing a program is broken downinto six basic steps.1. Statement. A statement forms a clear comprehensivestatement of the problem.2. Analysis. Analysis consists of laying out theproblem in a form that will lend itself to arithmeticaland/or logical analysis, determining what logicaldecision must be made, and if data manipulation isrequired.3. Flow diagram. A flow diagram, or chart, is anexpansion of the steps in which special symbols areused to represent the various operations to beperformed and the sequence in which they are to fall.4. Encoding. The process of converting theoperations listed in the flow chart into language thecomputer will use, either machine instructions, words,or compiler statements.5. Debugging. The process of locating errors inthe program is called “debugging.” Varioustechniques are available for this purpose. A programmay be written to include some aids for itself, or aseparate debugging program may be run to test theoperation of a malfunctioning program. For a simpleprogram, a trial solution may be done on paper, andthe computed results compared with those actuallyobtained at each step.6. Documentation. Documentation is veryimportant because later changes may be warranted ina program, or it may be desirable to use subroutinesfrom another program. Proper documentation willensure that this can be accomplished. Documentationshould include the following:l Program title. Problem statementFLOW CHARTINGThe programmer constructs a program “map” indetermining a solution to a problem. This map iscommonly called a flow chart and serves a multitudeof important functions. The flow chart maps thelogical steps required, decisions to be reached, andpaths to be followed as a result of the decisions.When properly annotated, it defines input/outputrequirements, address allocations, data accuracyconsiderations, and register usage. A flow chart isvaluable when debugging a program and whenmaking future changes.Flow charting can be constructed at various levelsof complexity. A high-level flow chart consists of afew symbols and presents a broad overview of theproblem. A low-level flow chart may approach aone-to-one correspondence between flow chartsymbol and program instruction. Usually, there willbe several flow charts for a program area. These maybe compared to the prints found in a maintenancemanual. These prints include a block diagram toshow the relationship of major units (high-level),functional block diagrams showing the major circuitsin a unit (intermediate-level), and the schematics ofthe circuits (low-level). Flow charts should beat sucha level that they will implement all the usespreviously discussed.MAINTENANCE PROGRAMSAs we have previously stated, a routine orprogram is a series of instructions that control theoperations of a computer. Each instruction is used tocause some action that is part of the overall task thecomputer must perform. Therefore, an instructionmay be considered as the basic building block of acomputer program.8-15