November
1998, Issue 100
Smart
Rocket
GRAB
THE KEY, HIT THE ROAD
Another
nice thing about bikes is they’re easy to work on, requiring
only a small set of basic tools. It’s the same with
the SX, thanks to the SX-Key from Parallax.
This
nifty gadget, shown in Photo 1, exploits the fact that
the SX has programming and debug logic onboard, accessed
via the OSC pins. In-system programming and debugging
for any SX-based design is a simple matter of incorporating
a four-pin header (OSC1, OSC2, power, ground). For programming,
the OSC pins act as a serial download channel, while
during debug, the SX-Key has explicit clock control.
|
(Click
here to enlarge)
|
Photo
1—Like the SX, the SX-Key development tool from
Parallax packs a lot of punch into a small package. |
Three
packages are offered for your riding pleasure. The Skeleton
Key ($249) is just the SX-Key and software tools. The
Master Key 18 ($319) adds a proto-board with buttons
and LEDs (see Photo 2a). The Master Key 28 ($349), shown
in Photo 2b, comes with a fully loaded demo board including
buttons, LEDs, RS-232, an external EEPROM, and a speaker.
|
a)
b)
(Click here to enlarge)
|
Photo
2a—Included in the Master Key packages, Parallax
offers a QuickProto board (with Master Key 18 package,
or $69 separately) and b—DemoBoard
(with Master Key 28, or $99 separately). |
On
the roads these days, there’s a remarkable proliferation
of SUVs. Folks seem to think they need a cross between
a Humvee and a Mack truck to get across town. It’s kind
of equivalent to the bloatware phenomenon that curses
our PCs.
Not
so with the SX-Key software (Win 95 and up), which is
blessedly simple, boiling down to three screens: one
for editing your ASM program, one for configuring the
SX, and the debug screens in Photo 3.
|
a)
b)
(Click
here to enlarge)
|
Photo
3a—The Parallax SX development software handles
configuration and programming of the chip. b—It
also handles debug of ASM programs. Notice the Parallax-defined
mnemonics and multiword macro instructions. |
The
set-up screen offers a good opportunity to top off the
SX feature list. You can see the variety of clock options
(crystal, resonator, RC, and internal 4 MHz with an
eight-stage divider), configurable brown-out reset,
extended stack (eight levels versus the usual two),
tweaked operation of the carry bit, optional input synchronizers
(metastability insurance at high clock rates), and so
on.
The
assembler uses the Parallax mnemonics popularized on
their earlier generation of PIC tools (there is a utility
available to convert existing PIC code to the SX/Parallax
mnemonics). Also, Parallax has defined a number of convenient
macro-instructions that consolidate common sequences
of single-word instructions into easier-to-use formats.
For
those of you so inclined, there’s a C compiler from
Byte Craft. Data-type support is impressive with 8-,
16-, 24- and 32-bit INTs, and even IEEE-754 floating
point, though I suspect it’s easy to bite off more than
a 2K-word SX can chew.
It’s
not cheap ($795 DOS, $1495 Win 95/98/NT), but I’ve always
found that C compilers embody that old axiom "you
get what you pay for."
One
open issue involves integration of the Byte Craft and
Parallax tools. At the time of this writing, they aren’t
really connected. However, both companies are planning
a cozier relationship.
