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Issue
99, October 1998
X-Y Graphing Data
Logger
by
Alberto Ricci Bitti
Start
• Machine
Muscle
• Using
Componentware
• Low-Power
Guys
• Flash
Risc Glue
• The Graphic
Engine
• Casio
Protocol
• Main
Code
• Inside
The Box
• Setting
up the Casio
• First
Graph
• Modeling
The Data
• Broader
Vision
• Software,
References & Sources
THE
GRAPHIC ENGINE
The Casio FX-9750G graphing
calculator has 32 KB of RAM for data or programs and a
64 ´ 128 black and white LCD. The FX-9750G is a member
of a larger family that includes models with color LCDs
and up to 64 KB of memory. It’s a powerful and enjoyable
math tool, but it costs about the same as a graphic LCD
module alone.
It runs on four LR03 batteries
for 200 h, and sensitive data and programs are maintained
for up to one year by a separate lithium battery. I’m
glad the Casio folks elected to use a standard miniature
stereo jack as the serial port connector for external
peripherals.
The data protocol is built
around a standard 9600-bps half-duplex serial stream,
with one start bit, two stop bits, and eight data bits
with no parity.
Interfacing the FX-9750G
to a PC is a matter of adapting TTL–to–RS-232
levels. A MAX232 can do the job. I built one of the dozens
of similar circuits I found on the Internet, coupled with
the FA-122 Windows backup software.
I haven’t tested the
compatibility with other calculators (besides the FX9750G),
but I don’t expect any differences in the protocol
between similar models.
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