The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Subroutines have two advantages. First, they help you to break up your program code
into discrete units, with each having a specific purpose. This makes the program code
easier to debug and easier to understand in general, especially if you return to it a week,
month, or year after writing it when the details are no longer fresh in your mind.
Second, subroutines make it easier to reuse your code if you have a similar task in
another project. For example, all or most of the code involved with controlling a display
module can usually be written as a subroutine, or perhaps a series of subroutines. This
way, if you want to use the same display module in more than one project, you can
reuse the code without having to pick through your previous programs to find the
program lines that you need.
• Keep program lines short. Short lines are easier to edit with BASIC-52’s line editor,
which requires retyping the entire line to make a change. They’re also easier to read. If
you upload programs from disk, shorter lines can eliminate problems caused by
BASIC-52’s not having enough time to process each line before the next one arrives.
Although BASIC-52 allows you to place multiple statements on one line, with up to 79
characters per line, shorter is better.
There are two situations where you might want to combine a series of short lines into
fewer, longer program lines: when the program has to execute as fast as possible, or
when you need to store the program in the smallest possible space. Even then, though,
you can develop the program with short lines, and combine them only after the program
is debugged and ready for permanent storage.
• Check syntax and spelling carefully. BASIC-52’s syntax consists of the rules of
grammar and punctuation that your program lines must follow. For example, a FOR
loop must include a variable, limits, and a NEXT instruction. Leave any of these out,
and your loop won’t work. There’s no room for spelling errors either. BASIC-52
doesn’t know that you meant LIST when you typed LSIT.
• Document your programs. Many of BASIC-52’s keywords aren’t too hard to
decipher. For example, it makes sense that the STOP instruction halts program
execution. But your own comments throughout the program can help you remember
why you wrote each program line, and what it’s supposed to accomplish.
BASIC-52 allows you to add comments, preceded by REM (remark). Try to write
comments that do more than just define the keywords in the line. Also explain the
purpose behind what you are doing. For example, this comment
10 REM read value from external memory
20 A=XBY(0FE00H)
Programming
does nothing more than define the BASIC-52 instruction that follows. In contrast,
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