Nuts & Volts

GETTING STARTED WITH PICs
BASIC ATOM
One of my favorite Microchip PIC
options is the Basic Atom. I’m sure
you’ve seen the Atom modules in
Nuts & Volts which have the same
footprint and look of the BASIC Stamp
modules, but what many people don’t
realize is at the heart of an Atom module
is actually a Microchip PIC16F876A
or PIC16F877A chip with a selfprogramming
bootloader inside. It’s a
PIC (Figure 2) that you can purchase
separately from the module and use in
your PIC16F877 or 876 circuit.
The story of the Basic Atom is
interesting. It was created by a couple
of guys in Michigan, only a few miles
away from where I live. They started
out by creating a PICBasic Pro compiler
competitor called the MBasic
compiler. It sold well, but had a lot of
early bugs. Because it was only two
guys, handling all the tech support
became a problem. They realized that
a lot of the tech support involved the
differences with the various PICs. If
they could focus on just a few key
PICs, they felt they could make a solid
compiler with the time they had.
The BASIC Stamp, being so popular,
became the footprint they tried to emulate,
but instead of using the fetch and
function BASIC Stamp method, they
took their MBasic compiler and combined
it with a custom bootloader program
for the PIC16F876 and PIC16F877.
These PIC chips have the unique ability
to program their own internal memory
with a small program hidden in their
program memory called a bootloader.
It’s kind-of like having an operating
system on your PC prior to loading a
program you really want to run.
The features of the MBasic compiler
were carried over to the Atom, so
this gives the Atom access to all the
PIC features, such as timers, A/D,
interrupts, etc. The Atom sold well
right from the start since it offered
higher speed and more memory. To
me, though, the big feature was the
fact that I could program the Atom
PIC chips and plug them into any PIC
16F876 or 877 development board.
If I designed my own development
■ FIGURE 3. The in-circut debugger
program screen shot.
board with a serial communication
circuit, similar to the RS232 circuit I
used in the March issue, then I could
program the Atom PIC 16F876 or 877
right in-circuit without having to
remove the PIC over and over again.
IN-CIRCUIT
DEBUGGER (ICD)
This is what locked me into the
Atom. The MBasic compiler had an
in-circuit debugger program (Figure 3)
built in that allowed you to run your
program in slow motion command by
command. This made it easy to catch
errors because you could see the
changes in the RAM (variables), special
function registers (timers, Portb,
etc.), and even run sections of program
in real time, but stop at a breakpoint.
It was like having a Basic language
driven emulator and it was included
for free and in the Atom software.
So, why would I be so excited about
all this and why am I telling you this?
It’s because they give away the Atom
compiler software for free. The only
catch is you have to buy the Atom PIC
chips from them or an authorized
reseller — like my site. The Atom chips
cost $20 each, so if you are going to
build a 100-piece design, then using the
PICBasic Pro compiler will quickly pay
for itself over the Atom, but most readers
are just experimenting or building a
few prototypes. For $20, you get a fullfeatured
compiler with in-circuit debugger
and features PICBasic Pro doesn’t
have, such as floating point math and
much simpler access to timers and
other special function registers.
Here is the best part of all. They
kept most of the syntax of the Basic
commands compatible with the BASIC
Stamp and PICBasic Pro, so moving a
program from the Stamp to PICBasic to
the Atom is quite easy. I often create
with the Atom using the ICD to prove
out the idea and then move to PICBasic
Pro for higher volume applications.
The Atom has been used by so
many people, it’s been proven to be a
very solid compiler. I recently released
my second book — this time on the
Atom — titled Programming the Basic
Atom Microcontroller. You should be
able to find it at the Nuts & Volts bookstore,
my website, and a few other
resellers. My point to all this is that
you still don’t have to spend more than
$50 to program PICs beyond the 31
command line limit, just like my
January article pointed out. I’ve even
put some of my Atom-based modules
on my website that are designed for
the beginner that wants a complete
development module with the
programming interface built in. I even
have my BasicBoard with LCD, LEDs,
switches, speaker, and potentiometer
April 2006 75