SHARPENING YOUR TOOLS OF CREATIVITY
PICAXE PRIMER
■ BY RON HACKETT
USING THE AXMATE POWER &
PROGRAMMING ADAPTER
In this month’s installment of the PICAXE Primer, we’re going to construct
a simple “AxMate” adapter that provides all the necessary breadboard
connections for powering and programming a PICAXE project. The AxMate
adapter simplifies the required connections to a breadboard-based project,
and its small size maximizes the space that’s available on a standard
breadboard for your actual PICAXE circuitry.
If you are a Nuts & Volts subscriber, you’re probably aware of the
Arduino line of microprocessors.
Arduinos may not be as inexpensive
or as easy to program as PICAXE
processors, but they do have some
very interesting and powerful
features. For example, most Arduino
projects can be implemented by
using a simple six-pin USB interface
that provides all the necessary
connections to power and program an
Arduino circuit. The USB-to-serial IC that
■ FIGURE 1.
Pinout for
the FTDI
USB to
Serial
Cable.
52
June 2010
is used in an Arduino programming
adapter is the FT232R from Future
Technology Devices International,
Ltd. This is the same chip that’s used
in the PICAXE AXE027 USB
programming cable, so when I first
became aware of the Arduino’s
single-cable breadboard connection, I
naively thought that I could simply
use the Arduino cable to power and
program my PICAXE projects.
Figure 1 presents the pinout of the
FTDI six-pin cable that I purchased
from Mouser.com in order to try it
with a PICAXE project. The CTS# and
RTS# lines are both handshaking
signals that are not used for PICAXE
programming, so I just connected the
+5V, Gnd, RxD, and TxD pins to a
simple 08M “Hello World” project as
shown in Figure 2. Note that the
directionality of the TxD and RxD
labels on the FTDI cable refer to the
cable’s “point of view.”
In other words, the cable’s TxD
line should be connected to the
08M’s SerIn (RxD) pin, and the
cable’s RxD line should be
connected to the 08M’s SerOut
(TxD) pin. Also, the cable’s TxD and
RxD lines have already been
converted to 5V TTL levels, so the
■ FIGURE 2. Breadboard Setup to
Test the FTDI Cable.
resistors in the circuit may not
actually be necessary. However, I
didn’t want to risk destroying
anything so I included them just to
be sure. As you can see in Figure 2, I
painted a red stripe on the +5V pin
to make sure I don’t accidentally
insert the cable’s connector upside-down. Also, it’s necessary to connect
the cable’s +5V and Gnd lines to
both power rails on the breadboard.
After double-checking all the
breadboard connections, I used the
Programming Editor to download a
simple LED blinking program to the
08M. Perhaps I should say I “tried to
use …” because it didn’t work. ProgEdit
informed me that the hardware was
not found! After re-checking all the
connections, I tried several more times
but just kept getting the same error
message. I spent some time searching
the archives of the PICAXE forum and
soon discovered the problem: the
AXE027 cable inverts the TxD and
RxD signals, but the FTDI cable does
not invert them. The documentation
for the AXE027 cable includes a
schematic that shows no indication
of either signal being inverted. This
led me to conclude that the inversion
is somehow implemented within the
FT232R IC itself, so I began searching
the FTDI website for clues. It turns
