Introduction to Arduino - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 4

complex. The microprocessor by itself was useless; it had to be hooked up to
external memory. To run a program on every boot, it had to also have read-only
memory. If you wanted interrupts, again, you had to add a chip into the design.
The end result was complicated and out of the reach of some enthusiasts. To do
without this complexity, enthusiasts that wanted programmable devices tended
to use what was already on their desk: a personal computer.
Most PCs at the time used the ISA bus, as shown in Figure 1-1. ISA was a
simple bus that allowed components to be added to the processor and general
computer system. It was a simple system that allowed users to insert add-on cards
into their computer, and it was extremely easy to use. It wasn't hard to create
a circuit board that could be plugged into an ISA slot, and complete prototyp-
ing boards existed, enabling enthusiasts and engineers to test a solution before
making their own board. Some of these boards even included breadboards, a
simple system allowing users to place their components and wires without the
need to solder. This sparked a small revolution, and many enthusiasts turned
to this type of board to do what previously could not be done: create program-
mable systems. An ISA board could have digital inputs and outputs, analog
inputs and outputs, radios, communication devices—just about anything was
possible. All this would be controlled by the computer's CPU, using simple
programming languages such as C or Pascal. My ISA card kept my student
apartment nice and warm by reading data from a thermometer and turning
on electric heaters, acting like a thermostat. It also served as an alarm clock,
programmed depending on my classes the next day. Although I did manage
to miss a few morning classes, in all fairness it was usually my fault; the ISA
card worked perfectly on a tight budget.
Figure 1-1: ISA prototyping board
Computers became faster, and systems evolved. The industry changed, and
so did the expansion ports. Just as enthusiasts became experts on the ISA bus,
the industry invented a new system: the VESA Local Bus (VLB). The VLB bus