Ax51 User's Guide

Modular Programming

Many programs are too long or complex to write as a single unit. Programming becomes much simpler when the code is divided into small functional units. Modular programs are usually easier to code, debug, and change than monolithic programs.

The modular approach to programming is similar to the design of hardware that contains numerous circuits. The device or program is logically divided into "black boxes" with specific inputs and outputs. Once the interfaces between the units have been defined, the detailed design of each unit can proceed separately.

The benefits of modular programming are:

• Efficient Program Development
  Programs can be developed more quickly with the modular approach since small subprograms are easier to understand, design, and test than large programs. With the module inputs and outputs defined, the programmer can supply the needed input and verify the correctness of the module by examining the output. The separate modules are then linked and located by the linker into an absolute executable single program module. Finally, the complete module is tested.
• Multiple Use of Subprograms
  Code written for one program is often useful in others. Modular programming allows these sections to be saved for future use. Because the code is relocatable, saved modules can be linked to any program which fulfills their input and output requirements. With monolithic programming, such sections of code are buried inside the program and are not so available for use by other programs.
• Ease of Debugging and Modifying
  Modular programs are generally easier to debug than monolithic programs. Because of the well defined module interfaces of the program, problems can be isolated to specific modules. Once the faulty module has been identified, fixing the problem is considerably simpler. When a program must be modified, modular programming simplifies the job. You can link new or debugged modules to an existing program with the confidence that the rest of the program will not change.