Hardware Reference
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was an extension to ISA, only adding a second connector for memory-mapped
I/O and Direct Memory Access (DMA), but it announced a change. Computers
were indeed getting faster, and some computer bus systems couldn't keep up.
Even VLB couldn't keep up, and after only a year, PCI became the reference.
The PCI bus is an advanced bus but requires components and logic to identify
itself. It suddenly became increasingly difi cult to create homemade boards.
Some users decided to use other industry-standard ports, such as the parallel
port or RS-232, but most stopped creating such systems. Those that did continue
mainly used analog systems or nonprogrammable digital systems. Instead of
having a programmable microcontroller, the system was designed using logic
gates. For example, a bulb could turn on if both inputs A and B were true, or
if input C was false. These tasks became more and more complicated as the
number of inputs increased.
Analog systems, such as radios and amplii ers, did not have a form of pro-
gramming. They were designed with a specii c task in mind. Coni guration
was analog; with a small screwdriver, the designer could “tweak” values with
potentiometers, variable resistances. It wasn't possible to program the device to
multiply an input signal by a specii c value; instead, potentiometers were added
to counter the effect of tolerances in the components. Designs therefore added
an additional phase, calibration. Specii c input signals were fed into devices,
and a specii c output was expected.
Processors did exist that could be used, and some projects did use them, but
integrating a processor into a design generally meant that several components
needed to be used. Memory chips, I/O controllers, or bus controllers had to be
used, even after a decade of technological advancements, and circuits became
more and more complicated. Even when designs worked, programming them
proved to be a challenge. Most programming was done via EEPROM devices,
short for Electronically Erasable Programmable Read-Only Memory. These
devices could contain a computer program and could be programmed using
an external programmer attached to a computer. They were called erasable
read-only because the contents could indeed be wiped and replaced, but doing
so required removal of the circuit and subjecting it to ultra-violet light for 20
minutes. One small error in a program could often take 30 minutes or more
to correct.
Atmel AVR
Atmel is an American semi-conductor company, founded in 1984, and the name
Atmel is an acronym for Advanced Technology for Memory and Logic. Right
from the start, Atmel designed memory chips that used less power than com-
peting designs, but it soon decided to create programmable devices. In 1994,
Atmel entered the microprocessor market, creating an extremely fast 8051-based
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