Tab Electronics Guide to Understanding Electricity ... - Sciences Club

Computers
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When an I/O port “sees” its specific address on the I/O bus, it will activate
for communication with the microprocessor. The microprocessor
will “look” at the various I/O ports as it is instructed to do so by the
running program. The functions of the I/O ports are defined by
firmware or software.
Programming Computers
Generally speaking, computers can be programmed at three different
levels. If you program the microprocessor directly using binary number
commands, the process is called machine-language programming (MLP).
This method is difficult and cumbersome, because the 16-bit digital
commands are not easily recognizable to a human.
The next programming level above MLP is called assembly-language
programming. When using assembly language, each binary number command
is replaced with an easier to understand mnemonic (pronounced
“nih-monic”). For example, instead of programming with commands like
0011010010011011, which is MLP, programming is performed with
mnemonics like ADD A,B, which instructs the microprocessor to add
the contents of the A and the B registers.
For long, complex programs, various high-level languages are used.
Common examples are Pascal, FORTRAN, APT, and many others. Highlevel
program languages are easy to use because they are very much like
human language. However, after the program is written, it must be converted
into MLP by a special computer program called a compiler.
Computer Processing of Analog Signals
When a computer needs to examine (or to output) a continuously variable
signal (referred to as analog or linear), the analog signal must be converted
into digital “words” before the microprocessor can understand it. Special
data acquisition I/O modules used for this purpose are called digital-to-analog
(D/A) converters or analog-to-digital (A/D) converters. A/D converters change
analog input levels into equivalent digital numbers, understandable to the
microprocessor. In contrast, D/A converters change digital words, from the
microprocessor, into equivalent voltage or current outputs.
The process of converting analog levels to digital words, and digital
words to analog levels, is called digitizing. To digitize an analog level, the
A/D converter actually divides the level into thousands of incremental