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ALL ABOUT MICROCONTROLLER CATEGORIES 439

Low- Level Programmable
The traditional way to program a microcontroller has been with assembly language, using
your PC as a host development system. Assembly language appears arcane to newcomers,
and for many it proves to be a stopping point in further study of microcontrollers. Making
matters more complex is that the assembly language for one brand of microcontroller is dif-
ferent from that for another.
Fortunately, most microcontrollers today can also be programmed with a more user- friendly
language, such as BASIC, C, or Pascal. These languages are much more approachable, mak-
ing them easier to learn. You might already know a little (or a lot) about one or more of these
languages, in which case you’re well on the road to programming a microcontroller. Software
on your computer converts your program into so- called machine code, which can be directly
read and used by the microcontroller (see Figure 35- 2).
An example of a microcontroller that is low- level programmable is the Arduino, which
actually uses the Atmel AVR (a popular 8- bit MCU) as its processor. As you’ll read in Chap-
ter 37, “Using the Arduino,” this microcontroller is more than just a chip. It takes a holistic
(whole system) approach that’s become very popular among robot builders and electronics
experimenters.

Integrated- Language Programmable
In this type of microcontroller, the chip itself contains a kind of language interpreter. A pro-
gram on your computer, a compiler, converts your program into an intermediate language
that uses “tokens” to represent actions. The interpreter inside the microcontroller finishes the
job of translating the tokens to the low- level code needed by the chip.
Examples of microcontrollers that use this approach include the BASIC Stamp and the
PICAXE. Both are based on 8- bit MCUs. These two controllers are further detailed in their
own chapters. See Chapter 38, “Using the PICAXE,” and Chapter 39, “Using the BASIC
Stamp.”

Choice of Programming Language
A low- level programmable microcontroller is basically a blank canvas; it’s up to you what you
put in it and how you do it. With these controllers you have an option of choosing the lan-
guage you wish to use. These include:

BASIC: This language is popular with those just starting out in programming, as the lan-
guage is designed for beginners— in fact, the B in BASIC stands for beginner. It’s also
a favorite among those already familiar with a BASIC language for the PC, such as
Visual Basic. BASIC is a more forgiving language than the others; for example, it’s not

Conversion to
machine code

Download of
Program machine code Figure 35- 2 Programming cycle
of a microcontroller. Programs are
developed on a PC, where they are
compiled to a machine- readable
format, and then downloaded
Microcontroller (usually via cable) to the
microcontroller.

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