Programming Microcontrollers In C:Program Description Language (PDL)

Program Description Language (PDL)

There are many methods that a programmer may choose to describe the algorithm to be implemented by a program. Flow charts have been used extensively in the past in many computer programming tasks. Although flow charts are useful, they tend to create an unstructured code and also a lot of time is usually wasted drawing them, especially when developing complex programs. In this section we shall be looking at a different way of describing the operation of a program, namely by using a program description language (PDL).

A PDL is an English-like language which can be used todescribe the operation of a program. Although there are many variants of PDL, we shall be using simple constructs of PDL in our programming exercises, as described below.

START-END

Every PDL program (or sub-program) should start with a START statement and terminate with an END statement. The keywords in a PDL code should be highlighted in bold to make the code more clear. It is also good practice to indent program statements between the PDL keywords.

Sequencing

For normal sequencing in a program, write the steps as short English text as if you are describing the program.

Example:

Turn on the valve Clear the buffer Turn on the LED

IF-THEN-ELSE-ENDIF

Use IF, THEN, ELSE, and ENDIF statements to describe the flow of control in your programs.

REPEAT-UNTIL

This is another useful control construct which can be used in PDL codes. An example is shown below where the program waits until a switch value is equal to1.

REPEAT

Turn on buzzer Read switch value

UNTIL switch = 1