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5 Program Structure And Layout
5.1 Modular Programming In C51
The first three editions of this work started this chapter with: "This is possibly not the place to
make the case for modular programming, but a brief justification might be appropriate."
However the interviening years have indicated that this is the place where the case for
modular programming must be made!
In anything but the most trivial programs the overall job of the software is composed of
smaller tasks, all of which must be identified before coding can begin. As an electronic
system is composed of several modules, each with a unique function, so a software system is
built from a number of discrete tasks. In the electronic case, each module is designed and
perfected individually and then finally assembled into a complete working machine.
With software there are many similar modeling techniques used for designing the structure
and modules of the code. A system, any system (properly applied) is better than no system.
At one time graphical modeling was the answer and this spawned CASE, Computer Aided
Software Engineering abd CAD, Computer Aided Design tools. They were expensive,
promised the earth..... and with CASE largely failed to deliver. Things have improved greatly.
Flow charts were in, then out and back in and some say never went away.
Firstly remember that
any tool is only as good
as the person using it.
You can make a
complete mess with or
without the design
tools tool (some would
say that the automated
tools help you make a
mess more eficiently).
For most 8051 designs
the software structures
can usually be drawn
using
paper
and
pencil.
I have only
used a tool in this case
for clarity of the
drawings.
Keyed Data
Customer
Cash Card
Message
Cash
Bank Service
Till
Account
Information
Print Slips
Bank
Transaction
Bank Computer
For the 8051, using mainly C or assembler, the structured or modular design methods should
be used. Structured or modular designed software is the C equivelent of the Object
Orientated Programming used with C++, Ada and the like. Both Structured and OO
programming share many concepts and good modular programming has many of the
attributes of OOP but due to the differences in the way the languages work can not have all of
them.
For the 8051 a structured method like Yourdon (one of the more popular) would be used.
The Yourden method has several views of the software and it is worth looking at these as an
example as to why modular programing should be used on all systems.
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