Nuts & Volts

⇒ PIC to PC Communication
⇒ As I write this, my first “Getting
Started with PICs” article has been published
and the email response has been
outstanding. Apparently, a lot of people
like the topic and want to know more
about getting started with PICs. Being
able to write these articles is really a joy
for me because I have a real passion for
programming PICs and I learned a lot of
it the hard way — via trial and error.
Having the chance to share my knowledge
with others is only beneficial,
though, if someone wants to read it.
The feedback email proves a lot of
people are reading. Feedback also
tells me what readers want to see,
and I can form my future articles
around that feedback. It’s just a great
example of two-way communication.
That’s also the topic of this month’s
column — communication.
Think about it. A major portion of
your monthly bills are dedicated to
communication — your phone bill
(both land line and cell), your cable TV
bill, your Internet bill, your magazine
subscriptions, books you buy, maybe
even a satellite radio bill — they are all
forms of communication we are
willing to pay for. This month, I want
to address one form of PIC-to-PC communication
using serial RS232 format,
and you get this one for free (excluding
the magazine subscription fee).
78 March 2006
Before I received my first computer
as a gift — a Commodore VIC20 —
I was fascinated with computer control.
Many years ago, I interfaced a circuit
built around a chip I found at
RadioShack, which made the VIC20 talk
via its expansion port. Nobody in my
family seemed to care too much, but I
was excited that I had figured out how
to control external electronics from a
computer. There have since been many
books written on how to use the parallel
port or serial port on a PC to control
electronics, and USB is taking over as
the communication port of choice.
Despite the USB revolution, the
RS232 serial port interface is still the
most common method of communicating
with various off-the-shelf
modules found in the pages of Nuts &
Volts. You can get RS232 style serial
LCDs, dataloggers, servo motor
controllers, and DC motor controllers,
just to name a few. You can also find
loads of Windows PC software all over
the web that will accept or send ASCII
data from the serial port.
Therefore, in my opinion, one of
the fundamental projects every PIC
by Chuck Hellebuyck
hobbyist should know is how to communicate
between a PIC and a PC serial
port. After that, you can add an RS232
to USB converter if you need USB.
GETTING STARTED
For this article, I wanted to keep it
simple and demonstrate how to have a
PC user control a bank of LEDs. By
entering the number on the PC, the user
can turn on a specific LED at a remote
location only connected to the PC by a
serial cable. The remote module will
have a PIC to handle the interface and
start the communication by sending a
message to the PC asking which LED to
light. The PC user enters their choice,
hits the “enter” key, and the PIC circuit
receives it and then lights the proper
LED. It’s simple two-way communication
with a functional purpose.
For the software — once again —
I turn to the PICBasic Pro sample
version to handle the software. At the
end of the article, though, I’ll address
some of the options for going beyond
the sample version’s limitation of 31
commands, as some email has