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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
FLASH
RISC GLUE
An eight-bit RISC microcontroller
glues the ADC to the Casio serial input. Because my goals
included rapid development time and low cost, I focused
on small flash- or EEPROM-based RISC microcontrollers.
The simplified RISC architecture
is easy to learn, and erasable parts let you concentrate
on the problem instead of the UV eraser. As a bonus, these
parts usually have simple, ultra-cheap PC-port-based programmers.
I chose the PIC16C84 (an
EEPROM part) and the newer PIC16F84 (an improved flash
version) from Microchip. A useful characteristic of the
PIC architecture is its support of data tables that are
as long as the program memory. This characteristic is
a result of the RETLW instruction.
These PICs are powerful enough
to handle serial communications entirely in software with
a 4-MHz clock. A faster part (you can find 50-MHz PIC
clones) is unnecessary.
The PIC draws only a few
microamps when sleeping (even with the watchdog timer
enabled), and best of all, it’s cheap and available.
MPLAB, a professional grade assembler and simulator, is
distributed for free by Microchip, along with lots of
useful libraries.
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